The document contains information about various thermodynamic concepts including: - Lattice enthalpy and how it is affected by ionic charge and radius. - Standard enthalpy of solution and hydration and factors that affect them such as charge and size of ions. - Entropy, the second law of thermodynamics, and how entropy increases during phase changes and temperature increases which leads to more disorder. - The relationship between free energy, enthalpy and entropy in determining spontaneity of reactions according to ΔG = ΔH - TΔS.

1. Matching Trios
Match the following words with the accompanying
definitions & examples or pictures YOU CAN CUT OR
MATCH WITH YOUR PEN

2. https://www.youtube.com/watch?v=99buqSVBuOo

3. Stations game / ANSWERS

4. 1. Which combination of ionic charge and ionic
radius give the largest lattice enthalpy for an ionic
compound?
Ionic charge Ionic radius
A. high large
B. high small
C. low small
D. low large

5. 2. The lattice enthalpy values for lithium fluoride and calcium
fluoride are shown below.
LiF(s) ∆Hο = +1022 kJ mol–1
CaF2(s) ∆Hο = +2602 kJ mol–1
Which of the following statements help(s) to explain why the value
for lithium fluoride is less than that for calcium fluoride?
I. The ionic radius of lithium is less than that of calcium.
II. The ionic charge of lithium is less than that of calcium.
A. I only
B. II only
C. I and II
D. Neither I nor II

6. 3. Which reaction has the most negative ∆Hο
value?
A. LiF(s) → Li+(g) + F–(g)
B. Li+(g) + F–(g) → LiF(s)
C. NaCl(s) → Na+(g) + Cl–(g)
D. Na+(g) + Cl–(g) → NaCl(s)

7. 4. Which type of reaction is referred to in the
definition of standard enthalpy change of
formation?
A. the formation of a compound from its
elements
B. the formation of a crystal from its ions
C. the formation of a molecule from its atoms
D. the formation of a compound from other
compounds

8. Enthalpies of solution and hydration
The standard enthalpy of solution
(DHsol
ө) is the enthalpy change
when one mole of an ionic
compound is dissolved in water to
produce aqueous ions.
Na+
(g) Na+
(aq)
The standard enthalpy of hydration (DHhyd
ө) is the enthalpy
change when one mole of gaseous ions is converted to one mole
of aqueous ions.
NaCl(s) Na+
(aq) + Cl–
(aq)

9. Calculating enthalpies of solution

10. Enthalpy of solution calculations

11. Factors affecting enthalpy of hydration
The size of the enthalpy of hydration depends on:
increasing
size
 The charge on the ion. The larger the charge on the ion,
the larger the enthalpy of hydration.
 The size of the ion. The smaller the ion, the larger the
enthalpy of hydration.
Li+
Na+
K+
–519
–406
–322
F–
Cl–
Br–
–506
–364
–335
Ion DHhyd (kJmol–1) Ion DHhyd (kJmol–1)
Ion DHhyd (kJmol–1) Ion DHhyd (kJmol–1)
Fe2+ Fe3+
–1950 –4430

12. What is a spontaneous reaction?

13. Entropy
Entropy is a measure of disorder, and is given the
symbol S. The units of S are: JK–1 mol–1.
 ordered  disordered
 low entropy  high entropy
 regular arrangement of
particles
 random arrangement of
particles

14. FREE ENERGY & ENTROPY
SPONTANEOUS CHANGES
- occur in one particular direction and not the other
- take place without the need for work
Exothermic reactions are usually spontaneous
- this is because they go from higher to lower enthalpy

15. FREE ENERGY & ENTROPY
SPONTANEOUS CHANGES
- occur in one particular direction and not the other
- take place without the need for work
Exothermic reactions are usually spontaneous
- this is because they go from higher to lower enthalpy
However ...
Why should reactions with a positive DH value take place spontaneously ?
(some salts dissolve readily in water and the solution gets colder, not hotter)
ENDOTHERMIC
Energy is put in to
overcome the
electrostatic
attraction between
ions

16. FREE ENERGY & ENTROPY
SPONTANEOUS CHANGES
- occur in one particular direction and not the other
- take place without the need for work
Exothermic reactions are usually spontaneous
- this is because they go from higher to lower enthalpy
However ...
Why should reactions with a positive DH value take place spontaneously ?
(some salts dissolve readily in water and the solution gets colder, not hotter)
ENDOTHERMIC
Energy is put in to
overcome the
electrostatic
attraction between
ions
EXOTHERMIC
Energy is released
as the ions are
attracted to polar
water molecules

17. FREE ENERGY & ENTROPY
SPONTANEOUS CHANGES
- occur in one particular direction and not the other
- take place without the need for work
Exothermic reactions are usually spontaneous
- this is because they go from higher to lower enthalpy
However ...
Why should reactions with a positive DH value take place spontaneously ?
(some salts dissolve readily in water and the solution gets colder, not hotter)
ENDOTHERMIC EXOTHERMIC
If the energy released when the ions dissolve is less than that put in to break up the lattice, the
overall process will be ENDOTHERMIC and the temperature of the solution will drop.

18. FREE ENERGY & ENTROPY
SPONTANEOUS CHANGES
- occur in one particular direction and not the other
- take place without the need for work
Exothermic reactions are usually spontaneous
- this is because they go from higher to lower enthalpy
However ...
Why should reactions with a positive DH value take place spontaneously ?
(some salts dissolve readily in water and the solution gets colder, not hotter)
This must mean that energy has to be put in for the reaction to take place

19. FREE ENERGY & ENTROPY
SPONTANEOUS CHANGES
- occur in one particular direction and not the other
- take place without the need for work
Exothermic reactions are usually spontaneous
- this is because they go from higher to lower enthalpy
However ...
Why should reactions with a positive DH value take place spontaneously ?
(some salts dissolve readily in water and the solution gets colder, not hotter)
This must mean that energy has to be put in for the reaction to take place
The answer is that enthalpy change DH does not give the full story.
Free energy changes, DG, give a better picture.

20. Entropy change for reactions

21. Predicting entropy changes

22. Syllable , Synonym, Antonym,
Discover the word in the bag
Explain your word using a:

23. Calculating entropy changes
Standard entropy changes for any chemical reaction or
physical change can be calculated using the following simple
expression:
Remember the following points:
 entropies of elements are not zero like DHf values, so they
should be included in calculations.
 the units of entropy, S, are JK–1 mol–1
DS = SSө
products – SSө
reactants
https://www.youtube.com/watch?v=Tay3-
2WKQ5Y&t=52s

24. Calculating entropy changes

25. Entropy change calculations

26. Entropy changes in the surroundings

27. Entropy changes in the surroundings

28. FREE ENERGY & ENTROPY
FREE ENERGY (G)
A reaction is only spontaneous if it can do work - it must generate free energy
A negative DG indicates a reaction capable of proceeding of its own accord

29. FREE ENERGY & ENTROPY
FREE ENERGY (G)
A reaction is only spontaneous if it can do work - it must generate free energy
A negative DG indicates a reaction capable of proceeding of its own accord
DG < 0 (- ive) Spontaneous reaction
DG > 0 (+ ive) Non-spontaneous reaction
(will be spontaneous in reverse direction)
DG = 0 The system is in equilibrium

30. FREE ENERGY & ENTROPY
FREE ENERGY (G)
A reaction is only spontaneous if it can do work - it must generate free energy
A negative DG indicates a reaction capable of proceeding of its own accord
DG < 0 (- ive) Spontaneous reaction
DG > 0 (+ ive) Non-spontaneous reaction
(will be spontaneous in reverse direction)
DG = 0 The system is in equilibrium
ENTROPY (S)
• Entropy (symbol S) is a measure of the disorder of a system
• The more the disorder, the greater the entropy
• If a system becomes more disordered, the value of DS is positive
• Values tend to be in JOULES - not kJ
DS = Sfinal - Sinitial

31. THE SECOND LAW
The Second Law of Thermodynamics is based on entropy and states that…
‘Entropy tends to a maximum’
This infers that... ‘all chemical and physical changes
involve an overall increase in entropy’

32. THE SECOND LAW
The Second Law of Thermodynamics is based on entropy and states that…
‘Entropy tends to a maximum’
This infers that... ‘all chemical and physical changes
involve an overall increase in entropy’
Entropy increases when • solids melt
• liquids boil
• ionic solids dissolve in water
• the number of gas molecules increases
• the temperature increases

33. THE SECOND LAW
The Second Law of Thermodynamics is based on entropy and states that…
‘Entropy tends to a maximum’
This infers that... ‘all chemical and physical changes
involve an overall increase in entropy’
Entropy increases when SOLIDS MELT
Regular arrangement
of particles in solids
Less regular arrangement;
more disorder in liquids

34. THE SECOND LAW
The Second Law of Thermodynamics is based on entropy and states that…
‘Entropy tends to a maximum’
This infers that... ‘all chemical and physical changes
involve an overall increase in entropy’
Entropy increases when LIQUIDS BOIL
Irregular arrangement;
some disorder in liquids
Random nature and disorder
of particles in a gas

35. THE SECOND LAW
The Second Law of Thermodynamics is based on entropy and states that…
‘Entropy tends to a maximum’
This infers that... ‘all chemical and physical changes
involve an overall increase in entropy’
Entropy increases when IONIC SOLIDS DISSOLVE IN WATER
Regular arrangement in
an ionic crystal lattice
Ions dissociate in water;
there is less order

36. THE SECOND LAW
The Second Law of Thermodynamics is based on entropy and states that…
‘Entropy tends to a maximum’
This infers that... ‘all chemical and physical changes
involve an overall increase in entropy’
Entropy increases when THE MOLES OF GAS INCREASE
Particles in gases move in a
random way. The more gas
molecules there are, the greater
the degree of randomness.

37. THE SECOND LAW
The Second Law of Thermodynamics is based on entropy and states that…
‘Entropy tends to a maximum’
This infers that... ‘all chemical and physical changes
involve an overall increase in entropy’
Entropy increases when THE TEMPERATURE INCREASES
Lower temperature; less
energy
Higher temperature; more
energy and more disorder

38. FREE ENERGY & ENTROPY
Free energy, enthalpy and entropy are related ... DG = DH - TDS
Special
case For a reversible reaction at equilibrium the value of DG is zero
If DG = ZERO then DH = T DS
and DS = DH
T
This occurs during changes of state (melting, boiling etc)

39. FREE ENERGY & ENTROPY
Free energy, enthalpy and entropy are related ... DG = DH - TDS
Special
case For a reversible reaction at equilibrium the value of DG is zero
If DG = ZERO then DH = T DS
and DS = DH
T
Worked Example
Calculate the entropy change when water turns to steam at 100°C (373K).
The enthalpy of vaporisation of water is +44 kJ mol-1
DS = DH = + 44 kJ mol -1 = + 118 J K -1 mol -1
T 373 K (+ive as gases have more disorder)
Entropy change values are much smaller than enthalpy
change values; they tend to be in Joules rather than kJ

41. 1. B
2. B
3. B
4. A
5. A
6. C
7. D
8. A
9. B
10. D
11. C
12. C
13. D
14. B
15. B
16. C
17. B
18. D
PART 1

42. 12. A
13. A
14. A
15. B
16. B
17. A
18. B
19. A
20. B
21. D
PART 2