IB Chemistry on Gibbs Free energy vs entropy on spontaneity

1. http://lawrencekok.blogspot.com
IB Chemistry on Gibbs Free Energy vs Entropy on
spontaneity.
Prepared by Prepared by
Lawrence Kok

2. E = sum kinetic energy/motion of molecule, and potential
energy represented by chemical bond bet atom
∆E = q + w
∆E = Change internal
energy
q = heat
transfer
w = work done
by/on system
Thermodynamics
Study of work, heat and energy on a system
∆E universe = ∆E sys + ∆E surrounding = 0
1st
Law Thermodynamics
Entropy - Measure of disorder
↓
∆S uni = ∆S sys + ∆S surr > 0 (irreversible rxn)
↓
All spontaneous rxn produce increase in entropy of universe
2nd
Law Thermodynamics
∆S uni = ∆S sys + ∆S surr
Isolated system - Entropy change of universe always increase
Click here thermodynamics entropy
Entropy
Measure molecular disorder/randomness
↓
More disorder - More dispersion of matter/energy
↓
More random - Rxn toward right- Entropy Increases ↑
Direction to right- Spontaneous to right →
2nd
Law
Thermodynamics
Embrace the chaos
Over time - Entropy increase ↑
Direction to left ← Never happen !
Click here thermodynamics
Energy cannot be created or destroyed
> 0

3. ∆S = Entropy
change
Entropy
Dispersal/Distribution
Matter Energy
Matter more disperse ↑
Entropy increases ↑
solid liquid gas
spontaneous - entropy ↑
Over time - Entropy increase ↑
Phase change - sol liq gas→ →
↓
Entropy increase ↑
Every energy transfer - increase entropy universe
Entropy universe can only go up - never go down
Entropy increase - many ways energy spread out
Dispersion energy as heat - increase entropy
Stoichiometry- more gas/liq in product
↓
Entropy increase ↑
T
Q
S =∆
Heat added ↑
Phase change Stoichiometry
Embrace the chaos
N2O4(g) 2NO→ 2(g)
1 2
2H2O(l) 2H→ 2 (g) + O2 (g)
1 2
3
3
More gas in product - Entropy ↑
Heat added ↑
Entropy
Measure molecular disorder/randomness
↓
More disorder - More dispersion of matter/energy
↓
More randon - Rxn towards right- Entropy Increases ↑
Liq more disorder than solid
Gas more disorder than liq
kinetic energy distributed
over wide range
Q = heat
transfer
T = Temp/K
Distribution matter in space Distribution energy bet particles
Direction to left ← Never happen !Direction to right- Spontaneous to right →

4. Statistical
Entropy
Entropy
Measure molecular disorder/randomness
↓
More disorder - More dispersion of matter/energy
↓
More random - Entropy Increases ↑
1st
Law Thermodynamics - Doesn't help explain direction of rxn
∆S uni > 0 (+ve) More disorder - spontaneous→
∆S uni < 0 (-ve) More order - non spontaneous→
Change sol liq gas - Higher entropy→ →
Greater number particles in product - Higher entropy
More complex molecule - More atoms bonded - Higher entropy
Higher temp - Vibrate faster - More random - Higher entropy
Why gas mixes and not unmix? Why heat flow from hot to cold?
Entropy
Notes on Entropy
1st
Law Thermodynamics 2nd
Law Thermodynamics
Energy cannot be created or destroyed
Transfer from one form to another
∆E universe = ∆E sys + ∆E surrounding = 0
Isolated system
↓
∆S uni always increase
∆E = q + w
Method to calculate entropy
Number microstates
Thermodynamic
Entropy
Heat + Temp involved
Gas mixesSolution diffuse Heat flow hot →cold
X X
X
∆E = internal
energy
q = heat
transfer
w = work done ∆S = Entropy
universe
∆S = Entropy
system
∆S = Entropy
surrounding
∆S uni = ∆S sys + ∆S surr
Law Thermodynamics
1 2
∆S = Entropy
uni
WkS ln=∆
∆S = Entropy
change
k = boltzmann
constant
W = Microstate
Click here statistical entropy Click here thermodynamics entropy
Why solution diffuse and not undiffuse?
Unit - J mol -1
K-1
surrsysuni SSS ∆+∆=∆
∆S = Entropy
sys and surr
High chaos factor

5. 1st
Law Thermodynamics - Doesn't help explain direction of rxn
∆S uni > 0 (+ve) More disorder - spontaneous→
∆S uni < 0 (-ve) More order - non spontaneous→
Change sol liq gas - Higher entropy→ →
Greater number particles in product - Higher entropy
More complex molecule - More atoms bonded - Higher entropy
Higher temp - Vibrate faster - More random - Higher entropy
Measure molecular disorder/randomness
↓
More disorder - More dispersion of matter/energy
↓
More random - Entropy Increases ↑
Isolated system
↓
∆S uni always increase
Entropy
Why gas mixes and not unmix? Why heat flow from hot to cold?
Notes on Entropy
1st
Law Thermodynamics 2nd
Law Thermodynamics
Energy cannot be created or destroyed
Transfer from one form to another
∆E universe = ∆E sys + ∆E surrounding = 0
∆E = q + w
Gas mixesSolution diffuse Heat flow hot →cold
X X
X
∆E = internal
energy
q = heat
transfer
w = work done ∆S = Entropy
universe
∆S = Entropy
system
∆S = Entropy
surrounding
∆S uni = ∆S sys + ∆S surr
Law Thermodynamics
3rd
Law Thermodynamics
Unit - J mol -1
K-1
Standard Molar Entropy, S0
Entropy perfectly crystal at 0K = 0
Std molar entropy, S0
(absolute value)
↓
S0
when substance heated from 0K to 298K
Std state - 1 atm / 1M sol
Temp = 298K
Std Molar Entropy/S0
S0
at 298 /JK-1
mol-1
Fe (s) + 27
H2O (s) + 48
Na (s) + 52
H2O (l) + 69
CH3OH (l) + 127
H2 (g) + 130
H2O (g) + 188
CO2 (g) + 218
Solid - Order
↓
Entropy Lowest
Liq - Less order
↓
Entropy Higher
Gas - Disorder
↓
Entropy Highest
Entropy highest
Why solution diffuse and not undiffuse?
High chaos factor

6. Entropy
Why gas mix and not unmix?Why solution diffuse and not undiffuse? Why heat flow from hot to cold?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Unit - J mol -1
K-1
Standard Molar Entropy, S0
Entropy perfectly crystal at 0K = 0 (Absolute value)
↓
S0
when substance heated from 0K to 298K
Std state - 1 atm / 1M sol
Temp = 298K
Std Molar Entropy/S0
S0
at 298 /JK-1
mol-1
Fe (s) + 27
H2O (s) + 48
Na (s) + 52
H2O (l) + 69
CH3OH (l) + 127
H2 (g) + 130
H2O (g) + 188
CO2 (g) + 218
Solid - Order
↓
Entropy Lowest
Liq - Less order
↓
Entropy Higher
Gas - Disorder
↓
Entropy Highest
Entropy
highest
Entropy
Standard Molar Entropy, S0
Depend on
Temp increase - Entropy increase↑ ↑
Physical/phase state
Dissolving solid Molecular mass
Click here thermodynamics entropy Ba(OH)2
Temp
Temp/K 273 295 298
S0
for H2 + 31 + 32 + 33.2
Sol Liq Gas - Entropy increase→ → ↑
State solid liquid gas
S0
for H2O + 48 + 69 + 188
entropy increase ↑ entropy increase ↑
Depend on
Substance NaCI NH4NO3
S0
for solid + 72 + 151
S0
for aq + 115 + 260
More motion - entropy increase ↑ Higher mass - entropy increase ↑
Substance HF HCI HBr
Molar mass 20 36 81
S0 + 173 + 186 + 198
S0
= 0 at 0K
All sub > 0K, have +ve S0

7. Entropy perfectly crystal at 0K = 0 (Absolute value)
↓
S0
when substance heated from 0K to 298K
Entropy
Why gas mix and not unmix?Why solution diffuse and not undiffuse? Why heat flow from hot to cold?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Unit - J mol -1
K-1
Standard Molar Entropy, S0
Std state - 1 atm / 1M sol
Temp = 298K
Std Molar Entropy/S0
S0
at 298 /JK-1
mol-1
H2O (s) + 48
Na (s) + 52
H2O (l) + 69
CH3OH (l) + 127
H2O (g) + 188
CO2 (g) + 218
Solid - Order
↓
Entropy Lowest
Liq - Less order
↓
Entropy Higher
Gas - Disorder
↓
Entropy Highest
Entropy
highest
Entropy
Standard Molar Entropy, S0
Depend on
Temp increase - Entropy increase↑ ↑
Physical/phase state
Dissolving solid Molecular mass
Temp
Temp/K 273 295 298
S0
for H2 + 31 + 32 + 33.2
Sol Liq Gas - Entropy increase→ → ↑
State solid liquid gas
S0
for H2O + 48 + 69 + 188
entropy increase ↑ entropy increase ↑
Depend on
More motion - entropy increase ↑
Click here entropy
notes
Click here entropy,
enthalpy free energy data
Click here entropy
CRC data booklet
Higher mass - entropy increase ↑
S0
= 0 at 0K
All sub > 0K, have +ve S0
Substance NaCI NH4NO3
S0
for solid + 72 + 151
S0
for aq + 115 + 260
Substance HF HCI HBr
Molar mass 20 36 81
S0 + 173 + 186 + 198

8. ∆Hf
θ
(reactant) ∆Hf
θ
(product)
Using Std ∆Hf
θ
formation to find ∆H rxn
∆H when 1 mol form from its element under std condition
Na(s) + ½ CI2(g) → NaCI(s) ∆Hf
θ
= - 411 kJ mol -1
Std Enthalpy Changes ∆Hθ
Std condition
Pressure
100kPa
Temp
298K
Conc 1M All substance
at std states
Std ∆Hf
θ
formation
Mg(s) + ½ O2(g) → MgO(s) ∆Hf
θ
=- 602 kJ mol -1
Reactants Products
O2(g) → O2 (g) ∆Hf
θ
= 0 kJ mol -1
∆Hrxn
θ
= ∑∆Hf
θ
(products) - ∑∆Hf
θ
(reactants)
∆Hf
θ
(products)∆Hf
θ
(reactants)
∆Hrxn
θ
Elements
Std state solid gas
2C(s) + 3H2(g)+ ½O2(g) → C2H5OH(I) ∆Hf
θ
=- 275 kJ mol -1
1 mole formed
H2(g) + ½O2(g) → H2O(I) ∆Hf
θ
=- 286 kJ mol -1
Std state solid gas 1 mol liquid
For element Std ∆Hf
θ
formation = 0
Mg(s)→ Mg(s) ∆Hf
θ
= 0 kJ mol -1
No product form
Using Std ∆Hf
θ
formation to find ∆H rxn
PDF version
Click here chem database
(std formation enthalpy)
Online version
Click here chem database
(std formation enthalpy)
C2H4 + H2 C2H6
Find ΔHθ
rxn using std ∆H formation
Reactants Products
2C + 3H2
Elements
C2H4 + H2 C→ 2H6
∆Hrxn
θ
∆Hrxn
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
∆Hrxn
θ
= Hf
θ
C2H6 - ∆Hf
θ
C2H4+ H2
= - 84.6 – ( + 52.3 + 0 ) = - 136.9 kJ mol -1
Enthalpy Formation, ∆Hf

9. Std ∆Gf
θ
formation
∆Grxn
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Grxn
θ
= Gf
θ
C2H6 - ∆Gf
θ
C2H4+ H2
= - 33 – ( + 68 + 0 ) = - 101 kJ mol -1
∆Gf
θ
(reactant) ∆Gf
θ
(product)
Using Std ∆Gf θ formation to find ∆G rxn o
∆Gf when 1 mol form from its element under std condition
Na(s) + ½ CI2(g) → NaCI(s) ∆Gf
θ
= - 384 kJ mol -1
Std Free Energy Change ∆Gθ
Std condition
Pressure
100kPa
Temp
298K
Conc 1M All substance
at std states
Gibbs Free Energy change formation, ∆Gf
Mg(s) + ½ O2(g) → MgO(s) ∆Gf
θ
=- 560 kJ mol -1
Reactants Products
O2(g) → O2 (g) ∆Gf
θ
= 0 kJ mol -1
∆Grxn
θ
= ∑∆Gf
θ
(prod) - ∑∆Gf
θ
(react)
∆Gf
θ
(product)∆Gf
θ
(reactant)
∆Grxn
θ
Elements
Std state solid gas
2C(s) + 3H2(g)+ ½O2(g) → C2H5OH(I) ∆Gf
θ
=- 175 kJ mol -1
1 mole formed
H2(g) + ½O2(g) → H2O(I) ∆Gf
θ
=- 237 kJ mol -1
Std state solid gas 1 mol liquid
For element Std ∆Gf
θ
formation = 0
Mg(s)→ Mg(s) ∆Gf
θ
= 0 kJ mol -1
No product form
Using Std ∆Gf
θ
formation to find ∆G rxn
PDF version
Click here chem database
(std ∆G formation)
Online version
Click here chem database
(std ∆G formation)
C2H4 + H2 C2H6
Find ΔGθ
rxn using std ∆G0
formation
Reactants Products
2C + 3H2
Elements
C2H4 + H2 C→ 2H6
∆Grxn
θ

10. ∆S sys + ve , ∆S surr - ve
↓
∆S uni > 0 (+ve)
(Rxn Spontaneous)
∆S sys - ve , ∆S surr + ve
↓
∆S uni < 0 (-ve)
(Rxn Non spontaneous)
spontaneous
+ve
-ve
=
S /JK-1
∆Ssys = + ve
∆Ssurr = + ve
∆Suni = + ve
+
∆Ssys = - ve
+
∆Ssurr = + ve
∆Suni = + ve
= spontaneous
S /JK-1
S /JK-1
∆Ssys = + ve
+
∆Ssurr = - ve
=
∆Suni = + ve
spontaneous
C6H12O6(s) + 6O2 (g) 6CO→ 2(g) + 6H2O(l)
Using ∆Hsys , ∆Suni , ∆Ssys , ∆S surr to predict spontaneity
2NO(g) + O2(g) 2NO→ 2(g) CaCO3 (s) CaO→ (s) + CO2(g)
∆H = -ve (Heat released)
Difficult !!
∆S sys + ve , ∆S surr - ve
↓
∆S uni < 0 (-ve)
(Rxn Non spontaneous)
∆Ssys = + ve
∆Ssurr = - ve
+
=
∆Suni = - ve
Non
spontaneous
∆H = -ve (Heat released) ∆H = +ve (Heat absorb)
CaCO3 (s) CaO→ (s) + CO2(g)
∆H = +ve (Heat absorb)
∆Ssys = + ve
+
∆Ssurr = - ve
∆Suni = - ve
Non
spontaneous
=
H2(g) 2 H→ (g)
∆H = +ve (Heat absorb)
H2O (l) H→ 2O(s)
∆H = -ve (Heat released)
∆Ssys = - ve
+
∆Suni = - ve
∆Ssurr = + ve
=
∆S sys + ve , ∆S surr - ve
↓
∆S uni < 0 (-ve)
(Rxn Non spontaneous)
∆S sys + ve , ∆S surr + ve
↓
∆S uni > 0 (+ve)
(Rxn Spontaneous)
∆S sys - ve , ∆S surr + ve
↓
∆S uni > 0 (+ve)
(Rxn Spontaneous)

11. ∆Hsys ∆Ssys ∆Suni Description
- + > 0 (+) Spontaneous, All Temp
+ - < 0 (-) Non spontaneous, All Temp
+ + > 0 (+) Spontaneous, High ↑ Temp
- - > 0 (+) Spontaneous, Low ↓ Temp
Predicting Spontaneity rxn
∆G - Temp/Pressure remain constant
Assume ∆S/∆H constant with temp
Using ∆Hsys , ∆Suni , ∆Ssys , ∆S surr to predict spontaneity Using ∆Gsys to predict spontaneity
syssyssys STHG ∆−∆=∆
Difficult !!
surrsysuni SSS ∆+∆=∆
T
H
Ssurr
∆−
=∆)()( reactfprofsys HHH ∆∑−∆∑=∆
CH4(g) + 2O2 (g) CO→ 2(g) + 2H2O(l)
CH4(g) + 2 O2 (g) CO→ 2(g) + 2 H2O(l)
∆Hf
0
- 74 0 - 393 - 286 x 2
S0
+ 186 +205 x 2 + 213 + 171 x 2
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
1
)tan()(
41
596555
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
kJHsys 891)74(965 −=−−−=∆
1
2990
298
)891000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
2949299041 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆S uni > 0
spontaneous
Easier
Unit ∆G - kJUnit ∆S - JK-1
Unit ∆H - kJ
CH4(g) + 2O2 (g) CO→ 2(g) + 2H2O(l)
Only ∆S sys involved
∆S surr, ∆S uni not needed
∆Hsys ∆Ssys ∆Gsys Description
- +
∆G = ∆H - T∆S
∆G = - ve
Spontaneous, All Temp
+ -
∆G = ∆H - T∆S
∆G = + ve
Non spontaneous, All Temp
+ +
∆G = ∆H - T∆S
∆G = - ve
Spontaneous, High ↑ Temp
- -
∆G = ∆H - T∆S
∆G = - ve
Spontaneous, Low ↓ Temp
CH4(g) + 2 O2 (g) CO→ 2(g) + 2 H2O(g)
S0
+ 186 +205 x 2 +213 + 188 x 2
Reactant (+596) Product (+589)
kJG
G
STHG syssyssys
888
)007.0(298890
−=∆
−−−=∆
∆−∆=∆
∆Hsys = - 890 kJ
kJS
JKS
S
SSS
sys
sys
sys
reactprodsys
007.0
7
596589
1
)()(
−=∆
−=∆
−=∆
−=∆
−
∆G < 0
spontaneous
Entropy change ∆S
greater at low temp

12. ∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= -868 - (-51) = - 817 kJ
Predicting Spontaneity rxn
∆G - Temp/Pressure remain constant
Assume ∆S/∆H constant with temp
Using ∆Gsys to predict spontaneity
syssyssys STHG ∆−∆=∆
CH4(g) + 2O2 (g) CO→ 2(g) + 2H2O(l)
Reactant (-51) Product (-868)
∆G < 0
spontaneous
Easier
Unit ∆G - kJ mol-1 CH4(g) + 2O2 (g) CO→ 2(g) + 2H2O(l)
Only ∆Ssys involved
∆S surr, ∆S uni not needed
∆Hsys ∆Ssys ∆Gsys Description
- +
∆G = ∆H - T ∆S
∆G = - ve
Spontaneous at all Temp
+ -
∆G = ∆H - T ∆S
∆G = + ve
Non spontaneous, all Temp
+ +
∆G = ∆H - T ∆S
∆G = - ve
Spontaneous at high ↑ Temp
- -
∆G = ∆H - T ∆S
∆G = - ve
Spontaneous at low ↓ Temp
CH4(g) + 2 O2 (g) CO→ 2(g) + 2 H2O(g)
S0
+ 186 +205 x 2 +213 + 188 x 2
Reactant (+ 596) Product (+ 589)
kJG
G
STHG syssyssys
888
)007.0(298890
−=∆
−−−=∆
∆−∆=∆
∆Hsys = - 890 kJ
kJS
JKS
S
SSS
sys
sys
sys
reactprodsys
007.0
7
596589
1
)()(
−=∆
−=∆
−=∆
−=∆
−
∆G < 0
spontaneous
Using ∆Gsys to predict spontaneity
Easier
CH4(g) + 2 O2 (g) CO→ 2(g) + 2 H2O(l)
∆G0
- 51 0 - 394 - 237 x 2
Method 1 Method 2
)()( reactfprofsys GGG °°
∆−∆=∆
CH4(g) + 2 O2 (g) CO2(g) + 2H2O(g)
C + 2O2 + 2H2
Reactants Products
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)Elements
• Neither ∆H or ∆S can predict feasibility of spontaneous rxn
• Gibbs Free Energy (∆G) – measure spontaneity and useful energy available
• Gibbs Free Energy (∆G) - max amt useful work at constant Temp/Pressure
• Involve ∆H sys and ∆S sys
• ∆G involve only sys while ∆S uni involve sys and surr
• Easier to find ∆H and ∆S for system
Gibbs Free Energy change formation, ∆Gf
0
At std condition/states
Temp - 298K
Press - 1 atm

13. ∆G - Temp/Pressure remain constant
Assume ∆S/∆H constant with temp
Using ∆Gsys to predict spontaneity
syssyssys STHG ∆−∆=∆
Easier
Unit ∆G - kJCH4(g) + 2O2 (g) CO→ 2(g) + 2H2O(l)
Only ∆S sys involved
∆S surr, ∆S uni not needed
∆Hsys ∆Ssys ∆Gsys Description
- +
∆G = ∆H - T∆S
∆G = - ve
Spontaneous, All Temp
+ -
∆G = ∆H - T∆S
∆G = + ve
Non spontaneous, All Temp
+ +
∆G = ∆H - T∆S
∆G = - ve
Spontaneous, High ↑ Temp
- -
∆G = ∆H - T∆S
∆G = - ve
Spontaneous, Low ↓ Temp
CH4(g) + 2 O2 (g) CO→ 2(g) + 2 H2O(g)
S0
+ 186 +205 x 2 +213 + 188 x 2
Reactant (+ 596) Product (+ 589)
kJG
G
G
STHG syssyssys
888
2890
)007.0(298890
−=∆
+−=∆
−−−=∆
∆−∆=∆
∆Hsys = - 890 kJ
kJS
JKS
S
SSS
sys
sys
sys
reactprodsys
007.0
7
596589
1
)()(
−=∆
−=∆
−=∆
−=∆
−
∆G < 0
spontaneous
Gibbs Free Energy Change, ∆G
∆G sys T∆S sys
Total energy change, ∆H
Measure spontaneity and useful energy available
Max amt useful work at constant Temp/Pressure
Free Energy
syssyssys STHG ∆−∆=∆
Free energy available
to do work not available
for work
syssyssys STHG ∆−∆=∆
Free Energy
Total energy change, ∆H
∆G sys T∆S sys
-890kJ
Free energy available
to do work
not available
for work
-888kJ +2 kJ

14. Gibbs Free Energy Change, ∆G
∆G - Temp/Pressure remain constant
Assume ∆S/∆H constant with temp
Using ∆Gsys to predict spontaneity
syssyssys STHG ∆−∆=∆
Easier
Unit ∆G - kJ mol-1
Only ∆Ssys involved
∆S surr, ∆S uni not needed
Using ∆Gsys to predict spontaneity
Easier
Method 1 Method 2
)()( reactfprofsys GGG °°
∆−∆=∆
At std condition/states
Temp - 298K
Press - 1 atm
Gibbs Free Energy change formation, ∆Gf
0
At High Temp ↑
Temp dependent
syssyssys STHG ∆−∆=∆
At low Temp ↓
veG
STG
HST sys
−=∆
∆−≈∆
∆>∆−
syssyssys STHG ∆−∆=∆
veG
HG
STH
−=∆
∆≈∆
∆−>∆
spontaneous spontaneous
surrsysuni SSS ∆+∆=∆
T
H
S
sys
surr
∆−
=∆
syssysuni STHST ∆−∆=∆−
Deriving Gibbs Free Energy Change, ∆G
T
H
SS
sys
sysuni
∆
−∆=∆
∆S sys / ∆H sys
multi by -T
syssyssys STHG ∆−∆=∆
∆Hsys ∆Ssys ∆Gsys Description
- +
∆G = ∆H - T ∆S
∆G = - ve
Spontaneous at all Temp
+ -
∆G = ∆H - T ∆S
∆G = + ve
Non spontaneous, all Temp
unisys STG ∆−=∆ syssyssys STHG ∆−∆=∆
Only ∆H sys/∆Ssys involved
∆S surr, ∆S uni not needed
°°°
∆−∆=∆ syssyssys STHG
Non standard conditionStandard condition
or
Gibbs Free Energy Change, ∆G
syssyssys STHG ∆−∆=∆unisys STG ∆−=∆
veGsys −=∆
∆Suni = +ve
Spontaneous Spontaneous
veGsys −=∆
∆H = - ve
∆S sys = +ve
∆Hsys ∆Ssys ∆Gsys Description
+ +
∆G = ∆H - T ∆S
∆G = - ve
Spontaneous at high ↑ Temp
- -
∆G = ∆H - T ∆S
∆G = - ve
Spontaneous at low ↓ Temp

15. kJG
G
STHG
130
)16.0(298178
+=∆
+−+=∆
∆−∆=∆
Predict entropy change - quatitatively
Reactant Product
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react) ∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
kJHsys 178)1206(1028 +=−−−=∆
∆G uni > 0 - Decomposition at 298K - Non Spontaneous
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
CaCO3 (s) CaO→ (s) + CO2(g)
CaCO3 (s) CaO→ (s) + CO2(g)
∆Hf
0
- 1206 - 635 - 393
S0
+ 93 + 40 + 213
kJS
S
S
SSS
sys
sys
sys
treacproductsys
16.0
160
93253
)tan()(
+=∆
+=∆
−=∆
−=∆
Decomposition at 298K Decomposition at 1500K
CaCO3 (s) CaO→ (s) + CO2(g)
CaCO3 (s) CaO→ (s) + CO2(g)
∆Hf
0
- 1206 - 635 - 393
S0
+ 93 + 40 + 213
kJHsys 178)1206(1028 +=−−−=∆
Rxn Temp dependent
Spontaneous at High temp↑
1500K
298K
Decomposition limestone
CaCO3 spontaneous?
Gibbs Free Energy Change, ∆G
kJS
S
S
SSS
sys
sys
sys
treacproductsys
16.0
160
93253
)tan()(
+=∆
+=∆
−=∆
−=∆
kJG
G
STHG
62
)16.0(1500178
−=∆
+−+=∆
∆−∆=∆
∆G uni < 0 - Decomposition at 1500K - Spontaneous
∆H = +ve
∆S = +ve
Temp dependent
∆Hsys ∆Ssys ∆Gsys Description
+ +
∆G = ∆H - T ∆S
∆G = - ve
Spontaneous at high ↑ Temp
- -
∆G = ∆H - T ∆S
∆G = - ve
Spontaneous at low ↓ Temp
At Low Temp At High Temp

16. Predict entropy change - quatitatively
Reactant Product
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react) ∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
∆G uni > 0 - Decomposition at 298K - Non Spontaneous
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
Rxn Temp dependent
Spontaneous at Low temp↓
298K (25C)
Gibbs Free Energy Change, ∆G
∆G uni < 0 - Decomposition at 1500K - Spontaneous
∆H = - ve
∆S = - ve
Temp dependent
∆Hsys ∆Ssys ∆Gsys Description
+ +
∆G = ∆H - T ∆S
∆G = - ve
Spontaneous at high ↑ Temp
- -
∆G = ∆H - T ∆S
∆G = - ve
Spontaneous at low ↓ Temp
H2O (l) H→ 2O(s)
H2O (l) H→ 2O(s)
∆Hf
0
- 286 - 292
S0
+ 70 + 48
Freezing at 298K (25C)
Is Freezing
spontaneous?
kJHsys 6)286(292 −=−−−=∆
kJS
S
S
SSS
sys
sys
sys
treacproductsys
02.0
22
7048
)tan()(
−=∆
−=∆
−=∆
−=∆
kJG
G
STHG
55.0
)022.0(2986
+=∆
−−−=∆
∆−∆=∆
Freezing at 263K (-10C)
H2O (l) H→ 2O(s)
H2O (l) H→ 2O(s)
∆Hf
0
- 286 - 292
S0
+ 70 + 48
kJHsys 6)286(292 −=−−−=∆
kJS
S
S
SSS
sys
sys
sys
treacproductsys
02.0
22
7048
)tan()(
−=∆
−=∆
−=∆
−=∆
263K (-10C) kJG
G
STHG
21.0
)022.0(2636
−=∆
−−−=∆
∆−∆=∆
At High Temp At Low Temp

17. C3H8(g) + 5 O2 (g) 3CO2(g) + 4H2O(l)
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
C3H8(g) + 5O2 (g) 3CO→ 2(g) + 4H2O(l) ∆H = -2220 kJ at 298K
C3H8(g) + 5 O2 (g) 3 CO→ 2(g) + 4 H2O(l)
S0
+270 +205 x 5 +213 x 3 +70 x 4
1295 919
Reactant Product
kJG
G
STHG
2108
)376.0(2982220
−=∆
−−−=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
376.0
376
1295919
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
∆H = -2220 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Is Combustion at
298K spontaneous?
Using Free Energy to predict spontaneity
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= -2130 - (-23) = - 2153 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G < 0 - Combustion at 298K - Spontaneous
C3H8(g) + 5 O2 (g) 3 CO→ 2(g) + 4 H2O(l)
∆G0
- 23 0 - 394 x 3 - 237 x 4
Elements
3C + 5O2 + 4H2
Reactant (-23) Product (-2130)
∆G < 0 - Combustion at 298K - Spontaneous

18. CH4(g) + 2O2 (g) CO→ 2(g) + 2H2O(g) ∆H = - 890 kJ at 298K
CH4(g) + 2 O2 (g) CO2(g) + 2H2O(g)
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
2
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 596 + 589
Reactant Product
kJG
G
STHG
888
)007.0(298890
−=∆
−−−=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
007.0
7
596589
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
∆H = - 890 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Is Combustion at
298K spontaneous?
Using Free Energy to predict spontaneity
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= -868 - (-51) = - 817 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G < 0 - Combustion at 298K - Spontaneous
CH4(g) + 2 O2 (g) CO→ 2(g) + 2 H2O(l)
∆G0
- 51 0 - 394 - 237 x 2
Elements
C + 2O2 + 2H2
Reactant (-51) Product (-868)
∆G < 0 - Combustion at 298K - Spontaneous
CH4(g) + 2 O2 (g) CO→ 2(g) + 2 H2O(g)
S0
+ 186 +205 x 2 +213 + 188 x 2

19. H2O (g) H→ 2O(l) ∆H = - 44.1 kJ at 298K
H2O(g) H2O(l)
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 188 + 70
Reactant Product
kJG
G
STHG
1.9
)118.0(2981.44
−=∆
−−−=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
118.0
118
18870
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
∆H = - 44.1 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= -237 - (-228) = - 9 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G < 0 - Combustion at 298K - Spontaneous
H2O(g) H→ 2O(l)
∆G0
-228 - 237
Elements
H2 + O2
Reactant (-228) Product (-237)
∆G < 0 - Combustion at 298K - Spontaneous
Condensation steam at
298K (25C) spontaneous?
H2O (g) H→ 2O(l)
S0
+ 188 + 70
3
Using Free Energy to predict spontaneity

20. H2(g) 2 H→ (g) ∆H = + 436 kJ at 298K
H2(g) 2H(g)
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 130 + 230
Reactant Product
kJG
G
STHG
406
)1.0(298436
+=∆
+−+=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
1.0
100
130230
1
)tan()(
+=∆
+=∆
−=∆
−=∆
−
∆H = + 436 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= + 406 - (0) = +406 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G > 0 - Atomization at 298K - Non Spontaneous
H2(g) 2H→ (g)
∆G0
0 + 203 x 2
Elements
H2
Reactant (0) Product ( + 406)
4Is Atomization of H2 at
298K spontaneous?
H2 (g) 2 H→ (g)
S0
+ 130 + 115 x 2
∆G > 0 - Atomization at 298K - Non Spontaneous
Using Free Energy to predict spontaneity

21. H2O (l) H→ 2O(s) ∆H = - 6 kJ at 298K
H2O(l) H2O(s)
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
2
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 70 + 48
Reactant Product
kJG
G
STHG
55.0
)022.0(2986
+=∆
−−−=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
022.0
22
7048
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
∆H = - 6 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= -236.6 - (-237) = + 0.4kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G > 0 -Freezing at 298K - Non Spontaneous
H2O(l) H→ 2O(s)
∆G0
-237 - 236.6
Elements
H2 + O2
Reactant (-237) Product (-236.6)
5
H2O (l) H→ 2O(s)
S0
+ 70 + 48
∆G > 0 -Freezing at 298K - Non Spontaneous
Is Freezing water to ice at
298K (25C) spontaneous?
Using Free Energy to predict spontaneity

22. H2O (l) H→ 2O(s) ∆H = - 6 kJ at 263K
H2O(l) H2O(s)
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
2
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 70 + 48
Reactant Product
kJG
G
STHG
21.0
)022.0(2636
−=∆
−−−=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
022.0
22
7048
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
∆H = - 6 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= -237.2 - (-237) = - 0.2 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G < 0 -Freezing at 263K - Spontaneous
H2O(l) H→ 2O(s)
∆G0
-237 - 237.2
Elements
H2 + O2
Reactant (-237) Product (-237.2)
6
H2O (l) H→ 2O(s)
S0
+ 70 + 48
∆G < 0 -Freezing at 263K - Spontaneous
Is Freezing water to ice at
263K (-10C) spontaneous?
Assume std condition
at 263K
Using Free Energy to predict spontaneity

23. CaCO3 (s) CaO→ (s) + CO2(g) ∆H = + 178 kJ at 298K
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 93 + 253
Reactant Product
kJG
G
STHG
130
)16.0(298178
+=∆
+−+=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
16.0
160
93253
1
)tan()(
+=∆
+=∆
−=∆
−=∆
−
∆H = + 178 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= - 999 - (- 1129) = + 130 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G > 0 - Decomposition at 298K - Non Spontaneous
CaCO3(s) CaO + CO→ 2(g)
∆G0
-1129 - 604 - 395
Elements
Ca + C + O2
Reactant ( -1129) Product (- 999)
7
Decomposition CaCO3 at
298K (25C) spontaneous?
CaCO3 (s) CaO→ (s) + CO2(g)
S0
+ 93 + 40 + 213
∆G > 0 - Decomposition at 298K - Non Spontaneous
CaCO3 (s) CaO (s) + CO2(g)
Using Free Energy to predict spontaneity

24. CaCO3 (s) CaO→ (s) + CO2(g) ∆H = + 178 kJ at 1500K
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 93 + 253
Reactant Product
kJG
G
STHG
62
)16.0(1500178
−=∆
+−+=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
16.0
160
93253
1
)tan()(
+=∆
+=∆
−=∆
−=∆
−
∆H = + 178 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= - 999 - (- 939) = - 60 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G < 0 - Decomposition at 1500K - Spontaneous
CaCO3(s) CaO + CO→ 2(g)
∆G0
-939 - 604 - 395
Elements
Ca + C + O2
Reactant (- 939) Product (- 999)
8
CaCO3 (s) CaO→ (s) + CO2(g)
S0
+ 93 + 40 + 213
CaCO3 (s) CaO (s) + CO2(g)
Decomposition CaCO3 at
1500K (1227C) spontaneous?
∆G < 0 - Decomposition at 1500K - Spontaneous
Assume std condition
at 1500K
Using Free Energy to predict spontaneity

25. 2NO(g) + O2(g) 2NO→ 2(g) ∆H = - 114 kJ at 298K
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 522 + 480
Reactant Product
kJG
G
STHG
101
)042.0(298114
−=∆
−−−=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
042.0
42
522480
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
∆H = - 114 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= + 104 - (174) = - 70 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G < 0 - Decomposition at 298K - Spontaneous
2 NO + O2 2NO→ 2(g)
∆G0
+ 87 x 2 0 + 52 x 2
Elements
N2 + O2
Reactant (+ 174) Product (+ 104)
9
2 NO(g) + O2 (g) 2NO2(g)
∆G < 0 - Decomposition at 298K - Spontaneous
Is Oxidation of NO at
298K (25C) spontaneous?
2 NO(g) + O2 (g) 2NO→ 2(g)
S0
+ 210 x 2 + 102 + 240 x 2
Using Free Energy to predict spontaneity

26. N2(g) + 3H2(g) 2NH→ 3(g) ∆H = - 92 kJ at 298K
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 585 + 384
Reactant Product
kJG
G
STHG
32
)2.0(29892
−=∆
−−−=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
2.0
201
585384
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
∆H = - 92 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= - 34 - (0) = - 34 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G < 0 - NH3 production at 298K - Spontaneous
N2 + 3H2 2NH→ 3(g)
∆G0
0 0 - 17 x 2
Elements
N2 + H2
Reactant (0) Product (- 34)
10
N2(g) + 3H2 (g) 2NH3(g)
Is Haber, NH3 production
298K (25C) spontaneous?
NH3
N2(g) + 3H2 (g) 2NH→ 3(g)
S0
+ 192 + 131 x 3 + 192 x 2
∆G < 0 - NH3 production at 298K - Spontaneous
Using Free Energy to predict spontaneity

27. Fe2O3(s) + 2AI(s) 2Fe→ (s) + AI2O3(s) ∆H = - 851 kJ at 298K
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 143 + 105
Reactant Product
kJG
G
STHG
840
)038.0(298851
−=∆
−−−=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
038.0
38
143105
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
∆H = - 851 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= -1576 - (-741) = - 835 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G < 0 - AI production at 298K - Spontaneous
Fe2O3 + 2AI 2Fe + AI→ 2O3
∆G0
- 741 0 0 - 1576
Elements
Fe + AI+ O2
Reactant (-741) Product (- 1576)
11Is Thermite, AI production
298K (25C) spontaneous?
Fe2O3(s) + 2AI(s) 2Fe→ (s) + AI2O3(s)
S0
+ 87 + 28 x 2 + 27 x 2 + 51
∆G < 0 - AI production at 298K - Spontaneous
Fe2O3(s) + 2AI(s) 2Fe(s) + AI2O3(s)
Using Free Energy to predict spontaneity

28. 4KCIO3(s) 3KCIO→ 4(s) + KCI(s) ∆H = - 144 kJ at 298K
Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 572 + 535
Reactant Product
kJG
G
STHG
133
)037.0(298144
−=∆
−−−=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
037.0
37
572535
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
∆H = - 144 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= -1317 - (-1160) = - 157 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G < 0 - Decomposition at 298K - Spontaneous
4KCIO3 3 KCIO→ 4 + KCI
∆G0
- 290 x 4 - 303 x 3 - 408
Elements
K + CI2 + O2
Reactant (-1160) Product (- 1317)
13
∆G < 0 - Decomposition at 298K - Spontaneous
Is decomposition KCIO3
298K (25C) spontaneous?
4KCIO3(s) 3KCIO→ 4(s) + KCI(s)
S0
+ 143 x 4 + 151 x 3 + 82
4KCIO3(s) 3KCIO4(s) + KCI(s)
Using Free Energy to predict spontaneity

29. Entropy and Gibbs Free Energy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Will rxn be spontaneous ?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
syssyssys STHG ∆−∆=∆
)tan()( treacprosys SSS ∑−∑=∆
+ 821 + 1698
Reactant Product
kJG
G
STHG
3071
)877.0(2982810
−=∆
+−−=∆
∆−∆=∆
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
877.0
877
8211698
1
)tan()(
+=∆
+=∆
−=∆
−=∆
−
∆H = - 2810 kJ
Assume ∆S, ∆H at constant over Temp
∆G sys < 0 (-ve) Spontaneous→
∆G sys > 0 (+ve) Non spontaneous→
Gibbs Free Energy, ∆G
syssyssys STHG ∆−∆=∆
Unit ∆S - JK-1
Unit ∆H - kJ
Unit ∆G - kJ
Reactants Products
∆Gsys
θ
= ∑∆Gf
θ
(pro) - ∑∆Gf
θ
(react)
∆Gsys
θ
= -3792 - (-910) = - 2882 kJ
∆Gsys
θ
∆Gf
θ
(reactant) ∆Gf
θ
(product)
)()( reactfprofsys GGG °°
∆−∆=∆
∆G < 0 Combustion sugar at 298K - Spontaneous
Elements
C + H2 + O2
Reactant (-910) Product (- 3792)
14
Is combustion sugar
298K (25C) spontaneous? C6H12O6(s) + 6O2 (g) 6CO→ 2(g) + 6H2O(l) ∆H = - 2810 kJ at 298K
C6H12O6 (s) + 6O2(g) 6CO→ 2(g) + 6H2O(l)
S0
+ 209 +102 x 6 + 213 x 6 + 70 x 6
∆G < 0 Combustion sugar at 298K - Spontaneous
C6H12O6 + 6O2 6CO2 + 6H2O(l)
C6H12O6 (s) + 6O2(g) 6CO→ 2(g) + 6H2O(l)
∆G0
- 910 0 - 395 x 6 - 237 x 6
Using Free Energy to predict spontaneity

30. Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Predict ∆G change - quatitatively
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Reactant Product
CH4(g) + 2O2 (g) CO→ 2(g) + 2H2O(l)
CH4(g) + 2 O2 (g) CO→ 2(g) + 2 H2O(l)
∆Hf
0
- 74 0 - 393 - 286 x 2
S0
+ 186 +205 x 2 +213 + 171 x 2
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
041.0
41
596555
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
kJHsys 890)74(964 −=−−−=∆
Is Combustion at
298K spontaneous?
Unit for ∆S - JK-1
Unit for ∆H - kJ C3H8(g) + 5O2 (g) 3CO→ 2(g) + 4H2O(l)
C3H8(g) + 5 O2 (g) 3 CO→ 2(g) + 4 H2O(l)
∆Hf
0
- 104 0 - 393 x 3 - 286 x 4
S0
+270 +205 x 5 + 213 x 3 + 171 x 4
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
028.0
28
12951323
1
)tan()(
+=∆
+=∆
−=∆
−=∆
−
kJHsys 2219)104(2323 −=−−−=∆
1 2
kJG
G
STHG
877
)041.0(298890
−=∆
−−−=∆
∆−∆=∆
∆G < 0 Combustion sugar at 298K - Spontaneous
kJG
G
STHG
881
)028.0(2982219
−=∆
+−−=∆
∆−∆=∆
∆G < 0 Combustion sugar at 298K - Spontaneous
Entropy and Gibbs Free Energy

31. Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Reactant Product
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
118.0
118
18870
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
kJHsys 44)242(286 −=−−−=∆
Is Condensation/Freezing at
298K spontaneous?
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
022.0
22
7048
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
kJHsys 6)286(292 −=−−−=∆
3 4H2O (g) H→ 2O(l) H2O (l) H→ 2O(s)
H2O (g) H→ 2O(l)
∆Hf
0
- 242 - 286
S0
+ 188 + 70
H2O (l) H→ 2O(s)
∆Hf
0
- 286 - 292
S0
+ 70 + 48
kJG
G
STHG
1.9
)118.0(2981.44
−=∆
−−−=∆
∆−∆=∆
∆G < 0 Condensation at 298K - Spontaneous
kJG
G
STHG
55.0
)022.0(2986
+=∆
−−−=∆
∆−∆=∆
∆G > 0 Freezing at 298K – Non Spontaneous
Entropy and Gibbs Free Energy
Predict ∆G change - quatitatively

32. Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Reactant Product
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
kJHsys 92)0(92 −=−−=∆
Are these rxn at
298K spontaneous?
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
kJHsys 168)1564(1732 −=−−−=∆
5 6N2(g) + 3H2(g) 2NH→ 3(g)
N2(g) + 3H2 (g) 2NH→ 3(g)
∆Hf
0
0 0 - 46 x 2
S0
+ 192 + 131 x 3 + 192 x 2
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
201.0
201
585384
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
4KCIO3(s) 3KCIO→ 4(s) + KCI(s)
4KCIO3(s) 3KCIO→ 4(s) + KCI(s)
∆Hf
0
- 391 x 4 - 432 x 3 - 436
S0
+ 143 x 4 + 151 x 3 + 82
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
037.0
37
572535
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
kJG
G
STHG
32
)2.0(29892
−=∆
−−−=∆
∆−∆=∆
∆G < 0 NH3 production at 298K - Spontaneous
kJG
G
STHG
157
)037.0(298168
−=∆
−−−=∆
∆−∆=∆
∆G < 0 KCIO3 production at 298K - Spontaneous
Entropy and Gibbs Free Energy
Predict ∆G change - quatitatively

33. Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Reactant Product
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react) ∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
kJHsys 178)1206(1028 +=−−−=∆
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
7 8CaCO3 (s) CaO→ (s) + CO2(g)
CaCO3 (s) CaO→ (s) + CO2(g)
∆Hf
0
- 1206 - 635 - 393
S0
+ 93 + 40 + 213
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
16.0
160
93253
1
)tan()(
+=∆
+=∆
−=∆
−=∆
−
Decomposition at 298K Decomposition at 1500K
CaCO3 (s) CaO→ (s) + CO2(g)
CaCO3 (s) CaO→ (s) + CO2(g)
∆Hf
0
- 1206 - 635 - 393
S0
+ 93 + 40 + 213
kJHsys 178)1206(1028 +=−−−=∆
Rxn Temp dependent
Spontaneous at High temp↑
1500K
298K (25C)
Decomposition limestone
CaCO3 spontaneous?
kJG
G
STHG
130
)16.0(298178
+=∆
+−+=∆
∆−∆=∆
∆G > 0 Decomposition at 298K – Non Spontaneous
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
16.0
160
93253
1
)tan()(
+=∆
+=∆
−=∆
−=∆
−
kJG
G
STHG
62
)16.0(1500178
−=∆
+−+=∆
∆−∆=∆
∆G < 0 Decomposition at 1500 K - Spontaneous
At Low Temp At High Temp
Entropy and Gibbs Free Energy
Predict ∆G change - quatitatively

34. Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Reactant Product
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react) ∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
022.0
22
7048
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
kJHsys 6)286(292 −=−−−=∆
Is Freezing
spontaneous?
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
kJS
JKS
S
SSS
sys
sys
sys
treacproductsys
022.0
22
7048
1
)tan()(
−=∆
−=∆
−=∆
−=∆
−
kJHsys 6)286(292 −=−−−=∆
9 10H2O (l) H→ 2O(s) H2O (l) H→ 2O(s)
H2O (l) H→ 2O(s)
∆Hf
0
- 286 - 292
S0
+ 70 + 48
H2O (l) H→ 2O(s)
∆Hf
0
- 286 - 292
S0
+ 70 + 48
Freezing at 298K (25C) Freezing at 263K (-10C)
Rxn Temp dependent
Spontaneous at Low temp↓
263K (-10C)298K (25C)
kJG
G
STHG
55.0
)022.0(2986
+=∆
−−−=∆
∆−∆=∆
∆G > 0 Freezing at 298K – Non Spontaneous
kJG
G
STHG
21.0
)022.0(2636
−=∆
−−−=∆
∆−∆=∆
∆G < 0 Freezing at 263K – Spontaneous
At High Temp At Low Temp
Entropy and Gibbs Free Energy
Predict ∆G change - quatitatively

35. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys decrease - More order - Less number gas↓
↓
Entropy surr increase - Heat release increase motion surr particles↑ ↑
↓
Heat release by sys to surr increase entropy surr↑
↓
∆S surr > ∆S sys (More +ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Combustion at 298K - Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
C3H8(g) + 5O2 (g) 3CO→ 2(g) + 4H2O(l) ∆H = -2220 kJ at 298K
C3H8(g) + 5 O2 (g) 3 CO→ 2(g) + 4 H2O(l)
S0
+270 +205 x 5 +213 x 3 +70 x 4
1295 919
Reactant Product
1
7450
298
)2220000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
376
1295919
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
70747450376 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = -2220 kJ
= -2220000J
surrsysuni SSS ∆+∆=∆
S /JK-1
Assume Q = H at constant pressure
+ve
-ve
spontaneous
∆Ssys = - 376
∆Ssurr = +7450
=+
∆Suni = + 7074
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Is Combustion at
298K spontaneous?

36. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys decrease - More order - Less number gas↓
↓
Entropy surr increase - Heat released increase motion surr particles↑ ↑
↓
Heat release by sys to surr increase entropy surr↑
↓
∆S surr > ∆S sys (More +ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Combustion at 298K - Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
CH4(g) + 2O2 (g) CO→ 2(g) + 2H2O(g) ∆H = - 890 kJ at 298K
CH4(g) + 2 O2 (g) CO→ 2(g) + 2 H2O(g)
S0
+ 186 +205 x 2 +213 + 188 x 2
+ 596 + 589
Reactant Product
1
2986
298
)890000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
7
596589
−
−=∆
−+=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
297929867 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = - 890 kJ
= - 890 000J
surrsysuni SSS ∆+∆=∆
S /JK-1
+ve
-ve
spontaneous
∆Ssys = - 7
∆Ssurr = + 2986
=+
∆Suni = + 2979
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Assume Q = H at constant pressure
Is Combustion at
298K spontaneous?

37. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys decrease - More order - Liquid form↓
↓
Entropy surr increase - Heat released increase motion surr particles↑ ↑
↓
Heat release by sys to surr increase entropy surr↑
↓
∆S surr > ∆S sys (More +ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Condensation at 298K - Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
H2O (g) H→ 2O(l) ∆H = - 44.1 kJ at 298K
H2O (g) H→ 2O(l)
S0
+ 188 + 70
+ 188 + 70
Reactant Product
1
148
298
)44100(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
118
18870
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
30148118 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = -44.1 kJ
= - 44 100J
surrsysuni SSS ∆+∆=∆
S /JK-1
spontaneous
∆Ssys = - 118
∆Ssurr = + 148
=+
∆Suni = + 30
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Condensation steam at
298K (25C) spontaneous?
Assume Q = H at constant pressure

38. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys increase - More disorder - More gas atoms form↑
↓
Entropy surr decrease - Heat absorb decrease motion surr particles↓ ↓
↓
Heat absorb by sys from surr decrease entropy surr↓
↓
∆S surr < ∆S sys (More -ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni < 0 - Atomization at 298K - Non Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
H2(g) 2 H→ (g) ∆H = + 436 kJ at 298K
H2 (g) 2 H→ (g)
S0
+ 130 + 115 x 2
+ 130 + 230
Reactant Product
1
1463
298
)436000(
−
−=∆
+−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
100
130230
−
+=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
13631463100 −
−=−+=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = + 436 kJ
= + 436 000J
surrsysuni SSS ∆+∆=∆
S /JK-1
+ve
-ve
non - spontaneous
∆Ssys = +100
∆Ssurr = - 1463
=+
∆Suni = - 1363
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Is Atomization of H2 at
298K spontaneous?
Assume Q = H at constant pressure

39. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys decrease - More order - Solid form↓
↓
Entropy surr increase - Heat released increase motion surr particles↑ ↑
↓
Heat release by sys to surr increase entropy surr↑
↓
∆S sys > ∆S surr (More -ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni < 0 - Freezing at 298K - Non Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
H2O (l) H→ 2O(s) ∆H = - 6 kJ at 298K
H2O (l) H→ 2O(s)
S0
+ 70 + 48
+ 70 + 48
Reactant Product
1
20
298
)6000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
22
7048
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
22022 −
−=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = -6 kJ
= - 6000J
surrsysuni SSS ∆+∆=∆
S /JK-1
+ve
-ve non - spontaneous
∆Ssys = - 22
∆Ssurr = + 20
=+
∆Suni= - 2
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Is Freezing water to ice at
298K (25C) spontaneous?
Assume Q = H at constant pressure

40. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys decrease - More order - Solid form↓
↓
Entropy surr increase - Heat released increase motion surr particles↑ ↑
↓
Heat release by sys to surr increase entropy surr↑
↓
∆S surr > ∆S sys (More +ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Freezing at 263K (-10C) - Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
H2O (l) H→ 2O(s) ∆H = - 6 kJ at 263K
H2O (l) H→ 2O(s)
S0
+ 70 + 48
+ 70 + 48
Reactant Product
1
8.22
263
)6000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
22
7048
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
8.08.2222 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = -6 kJ
= - 6000J
surrsysuni SSS ∆+∆=∆
S /JK-1
+ve
-ve
spontaneous
∆Ssys = - 22
∆Ssurr = + 22.8
=+
∆Suni= + 0.8
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Is Freezing water to ice at
263K (-10C) spontaneous?
Assume Q = H at constant pressure

41. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys increase - More disorder - Gas form↑
↓
Entropy surr decrease - Heat absorb decrease motion surr particles↓ ↓
↓
Heat absorb by sys from surr decrease entropy surr↓
↓
∆S surr < ∆S sys (More -ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni < 0 - Decomposition at 298K - Non Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
CaCO3 (s) CaO→ (s) + CO2(g) ∆H = + 178 kJ at 298K
CaCO3 (s) CaO→ (s) + CO2(g)
S0
+ 93 + 40 + 213
+ 93 + 253
Reactant Product
1
597
298
)178000(
−
−=∆
+−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
160
93253
−
+=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
437597160 −
−=−+=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = + 178 kJ
=+ 178 000J
surrsysuni SSS ∆+∆=∆
S /JK-1
+ve
-ve non - spontaneous
∆Ssys = + 160
∆Ssurr = - 597
=+
∆Suni= - 437
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Decomposition CaCO3 at
298K (25C) spontaneous?
Assume Q = H at constant pressure

42. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys increase - More disorder - Gas form↑
↓
Entropy surr decrease - Heat aborb decrease motion surr particles↓ ↓
↓
Heat absorb by sys from surr decrease entropy surr↓
↓
∆S sys > ∆S surr (More +ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Decomposition at 1500K - Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
CaCO3 (s) CaO→ (s) + CO2(g) ∆H = + 178 kJ at 1500K
CaCO3 (s) CaO→ (s) + CO2(g)
S0
+ 93 + 40 + 213
+ 93 + 253
Reactant Product
1
118
1500
)178000(
−
−=∆
+−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
160
93253
−
+=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
42118160 −
+=−+=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = + 178 kJ
=+ 178 000J
surrsysuni SSS ∆+∆=∆
S /JK-1
+ve
-ve
spontaneous
∆Ssys = + 160
∆Ssurr = - 118
=+
∆Suni = + 42
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Decomposition CaCO3 at
1500K (1227C) spontaneous?
Assume Q = H at constant pressure

43. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys decrease - More order - Less gas form↓
↓
Entropy surr increase - Heat release increase motion surr particles↑ ↑
↓
Heat release by sys to surr increase entropy surr↑
↓
∆S surr > ∆S sys (More +ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Oxidation at 298K - Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
2NO(g) + O2(g) 2NO→ 2(g) ∆H = - 114 kJ at 298K
2 NO(g) + O2 (g) 2NO→ 2(g)
S0
+ 210 x 2 + 102 + 240 x 2
+ 522 + 480
Reactant Product
1
382
298
)114000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
42
522480
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
33938242 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = - 114 kJ
= - 114 000J
surrsysuni SSS ∆+∆=∆
S /JK-1
+ve
-ve
spontaneous
∆Ssys = - 42
∆Ssurr = + 382
=+
∆Suni = + 339
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Is Oxidation of NO at
298K (25C) spontaneous?
Assume Q = H at constant pressure

44. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys decrease - More order - Less gas form↓
↓
Entropy surr increase - Heat release increase motion surr particles↑ ↑
↓
Heat release by sys to surr increase entropy surr↑
↓
∆S surr > ∆S sys (More +ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - NH3 production at 298K - Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
N2(g) + 3H2(g) 2NH→ 3(g) ∆H = - 92 kJ at 298K
N2(g) + 3H2 (g) 2NH→ 3(g)
S0
+ 192 + 131 x 3 + 192 x 2
+ 585 + 384
Reactant Product
1
308
298
)92000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
201
585384
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
107308201 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = - 92 kJ
= - 92 000J
surrsysuni SSS ∆+∆=∆
S /JK-1
+ve
-ve
spontaneous
∆Ssys = - 201
∆Ssurr = + 308
=+
∆Suni = + 107
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Is Haber, NH3 production
298K (25C) spontaneous?
Assume Q = H at constant pressure
NH3

45. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys decrease - More order↓
↓
Entropy surr increase - Heat release increase motion surr particles↑ ↑
↓
Heat release by sys to surr increase entropy surr↑
↓
∆S surr > ∆S sys (More +ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - AI production at 298K - Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
Fe2O3(s) + 2AI(s) 2Fe→ (s) + AI2O3(s) ∆H = - 851 kJ at 298K
+ 143 + 105
Reactant Product
1
2855
298
)851000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
38
143105
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
2817285538 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = - 851 kJ
= - 851 000J
surrsysuni SSS ∆+∆=∆
S /JK-1
+ve
-ve
spontaneous
∆Ssys = - 38
∆Ssurr = + 2855
=+
∆Suni = + 2817
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Is Thermite, AI production
298K (25C) spontaneous?
Assume Q = H at constant pressure
Fe2O3(s) + 2AI(s) 2Fe→ (s) + AI2O3(s)
S0 + 87 + 28 x 2 + 27 x 2 + 51

46. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys decrease - More order↓
↓
Entropy surr increase - Heat release increase motion surr particles↑
↓
Heat release by sys to surr increase entropy surr↑
↓
∆S surr > ∆S sys (More +ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Decomposition KCIO3 at 298K - Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
4KCIO3(s) 3KCIO→ 4(s) + KCI(s) ∆H = - 144 kJ at 298K
+ 572 + 535
Reactant Product
1
483
298
)144000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
37
572535
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
44648337 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = - 144 kJ
= - 144 000J
surrsysuni SSS ∆+∆=∆
S /JK-1
+ve
-ve
spontaneous
∆Ssys = - 37
∆Ssurr = + 483
=+
∆Suni = + 446
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Is decomposition KCIO3
298K (25C) spontaneous?
Assume Q = H at constant pressure
∆S/∆H constant over range of temp
4KCIO3(s) 3KCIO→ 4(s) + KCI(s)
S0 + 143 x 4 + 151 x 3 + 82

47. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Entropy
Thermodynamic Entropy
Gas mixesSolution diffuse Heat flow hot →cold
X X X
1
Quatitatively
T
H
T
Q
Ssurr
∆−
==∆
Quatitatively
Entropy sys increase - More disorder↑
↓
Entropy surr increase - Heat release increase motion particles↑ ↑
↓
Heat release by sys to surr increase entropy surr↑
↓
∆S surr + ∆S sys > 0 (More +ve)
↓
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 Combustion sugar at 298K - Spontaneous
surrsysuni SSS ∆+∆=∆
)tan()( treacprosys SSS ∑−∑=∆
C6H12O6(s) + 6O2 (g) 6CO→ 2(g) + 6H2O(l) ∆H = - 2810 kJ at 298K
+ 821 + 1698
Reactant Product
1
9430
298
)2810000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
1
)tan()(
877
8211698
−
+=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
103079430877 −
+=++=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆H = - 2810 kJ
= - 2810 000J
surrsysuni SSS ∆+∆=∆
S /JK-1
+ve
-ve
spontaneous
∆Ssys = + 877
∆Ssurr = + 9430
=+
∆Suni = + 10307
∆S uni > 0 (+ve) Spontaneous→
∆S uni < 0 (-ve) Non spontaneous→
Is combustion sugar
298K (25C) spontaneous?
Assume Q = H at constant pressure
∆S/∆H constant over range of temp
C6H12O6 (s) + 6O2(g) 6CO→ 2(g) + 6H2O(l)
S0 + 209 +102 x 6 + 213 x 6 + 70 x 6

48. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Predict entropy change - quatitatively
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Reactant Product
CH4(g) + 2O2 (g) CO→ 2(g) + 2H2O(l)
CH4(g) + 2 O2 (g) CO→ 2(g) + 2 H2O(l)
∆Hf
0
- 74 0 - 393 - 286 x 2
S0
+ 186 +205 x 2 + 213 + 70 x 2
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
1
)tan()(
243
596353
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
2990
298
)891000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
kJHsys 891)74(965 −=−−−=∆
surrsysuni SSS ∆+∆=∆
1
27472990243 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
Is Combustion at
298K spontaneous?
Unit for ∆S - JK-1
Unit for ∆H - kJ
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Combustion at 298K - Spontaneous
C3H8(g) + 5O2 (g) 3CO→ 2(g) + 4H2O(l)
C3H8(g) + 5 O2 (g) 3 CO→ 2(g) + 4 H2O(l)
∆Hf
0
- 104 0 - 393 x 3 - 286 x 4
S0
+270 +205 x 5 +213 x 3 + 70 x 4
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
1
)tan()(
376
1295919
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys kJHsys 2219)104(2323 −=−−−=∆
1
7446
298
)2219000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
surrsysuni SSS ∆+∆=∆
1
70707446376 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Combustion at 298K - Spontaneous
1 2

49. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Predict entropy change - quatitatively
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Reactant Product
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
1
)tan()(
118
18870
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
1
148
298
)44000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
kJHsys 44)242(286 −=−−−=∆
surrsysuni SSS ∆+∆=∆
1
30148118 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
Is Condensation/Freezing at
298K spontaneous?
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Condensation at 298K - Spontaneous
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
1
)tan()(
22
7048
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys kJHsys 6)286(292 −=−−−=∆
1
20
298
)6000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
surrsysuni SSS ∆+∆=∆
1
22022 −
−=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆S uni = ∆S sys + ∆S surr
↓
∆S uni < 0 -Freezing at 298K - Non Spontaneous
3 4H2O (g) H→ 2O(l) H2O (l) H→ 2O(s)
H2O (g) H→ 2O(l)
∆Hf
0
- 242 - 286
S0
+ 188 + 70
H2O (l) H→ 2O(s)
∆Hf
0
- 286 - 292
S0
+ 70 + 48

50. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Predict entropy change - quatitatively
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Reactant Product
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
1
308
298
)92000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
kJHsys 92)0(92 −=−−=∆
surrsysuni SSS ∆+∆=∆
1
107308201 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
Are these rxn at
298K spontaneous?
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - NH3 production at 298K - Spontaneous
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
kJHsys 168)1564(1732 −=−−−=∆
1
563
298
)168000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
surrsysuni SSS ∆+∆=∆
1
52656337 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Decomposition at 298K - Spontaneous
5 6N2(g) + 3H2(g) 2NH→ 3(g)
N2(g) + 3H2 (g) 2NH→ 3(g)
∆Hf
0
0 0 - 46 x 2
S0
+ 192 + 131 x 3 + 192 x 2
1
)tan()(
201
585384
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
4KCIO3(s) 3KCIO→ 4(s) + KCI(s)
4KCIO3(s) 3KCIO→ 4(s) + KCI(s)
∆Hf
0
- 391 x 4 - 432 x 3 - 436
S0
+ 143 x 4 + 151 x 3 + 82
1
)tan()(
37
572535
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys

51. 1
118
1500
)178000(
−
−=∆
+−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Predict entropy change - quatitatively
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Reactant Product
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
kJHsys 178)1206(1028 +=−−−=∆
surrsysuni SSS ∆+∆=∆
1
437597160 −
−=−+=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆S uni = ∆S sys + ∆S surr
↓
∆S uni < 0 - Decomposition at 298K - Non Spontaneous
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
surrsysuni SSS ∆+∆=∆
1
42118160 −
+=−+=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 - Decomposition at 1500K - Spontaneous
7 8CaCO3 (s) CaO→ (s) + CO2(g)
CaCO3 (s) CaO→ (s) + CO2(g)
∆Hf
0
- 1206 - 635 - 393
S0
+ 93 + 40 + 213
1
)tan()(
160
93253
−
+=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys
Decomposition at 298K Decomposition at 1500K
CaCO3 (s) CaO→ (s) + CO2(g)
CaCO3 (s) CaO→ (s) + CO2(g)
∆Hf
0
- 1206 - 635 - 393
S0
+ 93 + 40 + 213
1
)tan()(
160
93253
−
+=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys kJHsys 178)1206(1028 +=−−−=∆
Rxn Temp dependent
Spontaneous at High Temp↑
1500K (1227C)298K (25C)
Decomposition limestone
CaCO3 spontaneous?
1
597
298
)178000(
−
−=∆
+−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr

52. Entropy
Why gas mixes and not unmix?Why conc solution diffuse and not undiffuse? Why heat flow from hot to cold?
Predict entropy change - quatitatively
Gas mixesSolution diffuse Heat flow hot →cold
X X X
Reactant Product
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
1
)tan()(
22
7048
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys kJHsys 6)286(292 −=−−−=∆
surrsysuni SSS ∆+∆=∆
1
22022 −
−=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
Is Freezing
spontaneous?
∆S uni = ∆S sys + ∆S surr
↓
∆S uni < 0 - Freezing at 298K - Non Spontaneous
Reactant Product
∆Ssys
θ
= ∑Sf
θ
(pro) - ∑Sf
θ
(react)
∆Hsys
θ
= ∑∆Hf
θ
(pro) - ∑∆Hf
θ
(react)
1
)tan()(
22
7048
−
−=∆
−=∆
−=∆
JKS
S
SSS
sys
sys
treacproductsys kJHsys 6)286(292 −=−−−=∆
1
8.22
263
)6000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
surrsysuni SSS ∆+∆=∆
1
8.08.2222 −
+=+−=∆
∆+∆=∆
JKS
SSS
uni
surrsysuni
∆S uni = ∆S sys + ∆S surr
↓
∆S uni > 0 -Freezing at 263K - Spontaneous
9 10H2O (l) H→ 2O(s) H2O (l) H→ 2O(s)
H2O (l) H→ 2O(s)
∆Hf
0
- 286 - 292
S0
+ 70 + 48
H2O (l) H→ 2O(s)
∆Hf
0
- 286 - 292
S0
+ 70 + 48
Freezing at 298K (25C)
Freezing at 263K (-10C)
Rxn Temp dependent
Spontaneous at Low temp↓
1
20
298
)6000(
−
+=∆
−−
=∆
∆−
=∆
JKS
S
T
H
S
surr
surr
surr
263K (-10C)298K (25C)