General Summary of Thermodynamics
FIRST LAW OF
THERMODYNAMICS:
The total amount of energy (and
mass) in the universe is constant.
That is, in any process energy can
be changed from one form to
another; but, it can never be
created nor destroyed.
“ You can’t get something for
nothing”
SECOND LAW OF
THERMODYNAMICS:
In any spontaneous process the
entropy of the universe increases:
Suniverse = Ssystem + Ssurroundings
or
Suniverse -Ssurroundings = Ssystem
(Variant)In trying to do work, you
always lose energy to the
surroundings.
“You can’t even break even!”
THIRD LAW OF
THERMODYNAMICS:
Any pure crystalline substance at
a temperature of absolute zero
(0.0K) has an entropy of zero
(S = 0.0 J/K-mol).
Terminology:
Energy = capacity to do work
System = portion of the universe we are considering
Open system = energy and matter can transfer
Closed system = energy transfers
Isolated system = no transfers
Surroundings = everything else besides the system
Isothermal = system at constant temperature
Heat capacity = amt. of heat required to raise the temperature of a
certain amt. of material by 1C or 1K.
Calorie = amt. of heat required to raise the temperature of 1g of water
by 1ºC.
Signs:
H >0 or (+) heat absorbed (endo)
H <0 or (-) heat released (exo)
S >0 or (+) entropy increasing (becoming disordered)
S <0 or (-) entropy decreasing (becoming ordered)
G >0 or (+) nonspontaneous Kc <1
G = 0, Kc = 1
G < 0 or (-) spontaneous Kc >1
Rules about Entropy: (Entropy increases)
1. w/ increasing temperature*
2. as one goes from s -> l -> aq ->g*
3. if a solid or liquid is dissolved in a solvent*
4. number of particles increases*
5. mass of the molecule increases
6. Entropy is higher for weakly bonded materials than for strong
covalent materials
7. As complexity of a molecule increases.
FORMULA’S:
G = H- TS (T in K = 273 + C)
T = H/S (assume G = 0 or when Kc = 1, like fusion/vaporization)
Hrxn = (#mol.) *(Hf(products)) - (#mol.) *(Hf(reactants)) = kJ
Srxn = (#mol.) *(S(products)) - (#mol.) *(S(reactants) ) = J/K (Watch Out -> J to kJ)
Grxn = (#mol.) *(Gf(products)) - (#mol.) *(Gf(reactants)) = kJ
G = -RTlnKc or Kc = e
-(G/RT)
Remember: e
x
is 2
nd
function natural log (ln) on calculator and work inside-out
H S G
+ + (+/-) (Spont. Only at High Temp. when TS > H)
- + - (Spontaneous at ALL Temperatures)
- - (+/-) (Spont. Only at Low Temp. when TS < H)
+ - + (Non-spontaneous at ALL Temperatures)
G = H- TS when G is – gives a spontaneous
reaction
Enthalpy (H): The Energy of motion or transition.
q is the heat measured from a reaction. If rxn is at constant pressure q = H
.
2. FIRST LAW OF
THERMODYNAMICS:
The total amount of energy (and
mass) in the universe is constant.
That is, in any process energy can
be changed from one form to
another; but, it can never be
created nor destroyed.
“ You can’t get something for
nothing”
SECOND LAW OF
THERMODYNAMICS:
In any spontaneous process the
entropy of the universe increases:
or
iverse -
3. (Variant)In trying to do work, you
always lose energy to the
surroundings.
“You can’t even break even!”
THIRD LAW OF
THERMODYNAMICS:
Any pure crystalline substance at
a temperature of absolute zero
(0.0K) has an entropy of zero
(S = 0.0 J/K-mol).
Terminology:
Energy = capacity to do work
System = portion of the universe we are considering
Open system = energy and matter can transfer
Closed system = energy transfers
Isolated system = no transfers
Surroundings = everything else besides the system
Isothermal = system at constant temperature
4. Heat capacity = amt. of heat required to raise the temperature
of a
certain amt. of material by 1C or 1K.
Calorie = amt. of heat required to raise the temperature of 1g
of water
by 1ºC.
Signs:
-) heat released (exo)
-) entropy decreasing (becoming ordered)
or (+) nonspontaneous Kc <1
-) spontaneous Kc >1
Rules about Entropy: (Entropy increases)
1. w/ increasing temperature*
2. as one goes from s -> l -> aq ->g*
3. if a solid or liquid is dissolved in a solvent*
4. number of particles increases*
5. mass of the molecule increases
6. Entropy is higher for weakly bonded materials than for strong
covalent materials
5. 7. As complexity of a molecule increases.
FORMULA’S:
-
fusion/vaporization)
-
- l.)
-> J to kJ)
-
-RTlnKc or Kc = e
-
Remember: e
x
is 2
nd
function natural log (ln) on calculator and work inside-out
+ + (+/-
- + - (Spontaneous at ALL Temperatures)
6. - - (+/-
+ - + (Non-spontaneous at ALL Temperatures)
- – gives a spontaneous
reaction
q is the heat measured from a reaction. If rxn is at constant
pressure q = H
q is measured experimentally by calorimetry where qsystem = (-
)qsurroundings
here you maybe calc qsys,
if qsystem = positive number (absorbing heat) it comes from the
surroundings where
qsystem = (-)qsurroundings
Hess' Law: The addition of several reactions to obtain a
"desired" overall reaction. If a reaction
multiplied by a coefficient, then also
appear on both sides of the
7. equation and do not appear in the "desired" equation.
Enthalpy is a stoichiometric quantity: The amount of heat is
proportional to the number of
moles of reactants/products.
Entropy: The measure of disorder of the system.
Entropy can NOT be experimentally measured directly.
1
st
, look for changes in physical states (s, l, aq, g) from reactants
to products.
2
nd
, look for changes in the number of moles of reactants to moles
of products.
Standard States Conditions:
Solution
8. s: 1 M; Partial Pressures: 1 atm;
Temperatures are generally at 25°C (298 K)
Gibbs' Free Energy: Amount of Energy left over fr
“price” one must pay to do work.
Enthalpy, Entropy, and Gibb's Free Energy are all state
functions. State functions depend only
on the final and initial states of a process.
(products) - initial state (reactants).
Consider non-equilibrium conditions:
One can calculate Gibb's Free Energy for non-equilibrium
conditions using Q from Equilibium
rxn + RT ln(Q)
- ) move toward
becomes less positive until it reaches zero-equilibrium.
9. - RT ln(K) (where R =
8.314 J/(Kmol) and K = equil.
constant (WATCH OUT for units: R has units Joules, but
where 1000 J = 1 kJ.
Thermodynamic Data at 298.15 K (25°C)
