1. Thermodynamics
Chapter 19

2. Spontaneous Processes and Entropy
Thermodynamics lets us predict whether a process will occur but gives no information about the amount of time required for the process.
A spontaneous process is one that occurs without outside intervention.

3. Figure: 19-03

5. Entropy
The driving force for a spontaneous process is an increase in the entropy of the universe.
Entropy, S, can be viewed as a measure of randomness, or disorder.

6. Figure: 19-05

8. Figure: 19-08

9. Ssolid < Sliquid << Sgas
Positional Entropy
A gas expands into a vacuum because the expanded state has the highest positional probability of states available to the system.
Therefore,
Ssolid < Sliquid << Sgas

10. Figure: 19-14

11. The Second Law of Thermodynamics
. . . in any spontaneous process there is always an increase in the entropy of the universe.
Suniv > 0
for a spontaneous process.

12. Figure: 19-11a,b

14. G means +Suniv Free Energy
G = H  TS (from the standpoint of the system)
A process (at constant T, P) is spontaneous in the direction in which free energy decreases:
G means +Suniv

15. Effect of H and S on Spontaneity

16. Figure: 19-T04

17. The Third Law of Thermodynamics
. . . the entropy of a perfect crystal at 0 K is zero.
Because S is explicitly known (= 0) at 0 K, S values at other temps can be calculated.

18. Free Energy Change and Chemical Reactions
G = standard free energy change that occurs if reactants in their standard state are converted to products in their standard state.
G = npGf(products)  nrGf(reactants)

19. Entropy and Enthalpy

20. Free Energy and Pressure
G = G + RT ln(Q)
Q = reaction quotient from the law of mass action.

21. Free Energy and Equilibrium
G = RT ln(K)
K = equilibrium constant
This is so because G = 0 and Q = K at equilibrium.

24. Figure: 19-18

25. Temperature Dependence of K
ln(K) = -Ho/R*(1/T) + So/R
y = mx + b
(H and S  independent of temperature over a small temperature range)

26. Reversible v. Irreversible Processes
Reversible: The universe is exactly the same as it was before the cyclic process.
Irreversible: The universe is different after the cyclic process.
All real processes are irreversible -- (some work is changed to heat).

27. END