1. Gibbs Free Energy

2. How can we use ΔH and ΔS to predict whether a given reaction occuring at constant temperature and pressure will be spontaneous?

3. Gibbs Free Energy (G)
State Function
ΔG is equivalent to -TΔSuniverse

4. Gibbs Free Energy If Suniv > 0 , G < 0 ( spontaneous rxn)
If G > 0 (nonspontaneous rxn)
If G = 0 (rxn at equilibrium )

5. Effect of Temperature on Free Energy

6. Free energy always decreases for any spontaneous process carried out at constant temperature and pressure

7. In terms of K and Q Q<K excess of reactants relative to products
Reaction spontaneous in forward direction
Q > K excess of products relative to reactants
Reaction is spontaneous in reverse direction
Q = K at equilibrium
K = equilibrium constant, reactant vs. product favored
Q = reaction quotient = plug in concentrations at a given time during reaction

8. Calculating Gibbs Free Energy
3 equations to use:

9. Gibb’s Free Energy Practice Problem 1

10. Problem 1 Answer

11. Problem 1 Answer Cont.

12. Standard free energy of formation Δ Gof
For a pure element Δ Gof = 0
For a solution assume 1 M concentration

13. Practice Problem 2
Use data from Appendix C to calculate the standard free-energy change for the reaction below.
P4 (g) + 6 Cl2(g)  4 PCl3 (g)
Answer = kJ

14. Free Energy and Equilibrium under non standard conditions
G = G + RT lnQ
(Under standard conditions, all concentrations are 1 M, so Q = 1 and lnQ = 0; the last term drops out.)

15. Practice Problem 3
Calculate Δ G at 298 K for a mixture of 1.0 atm N2, 3.0 atm H2, and 0.50 atm NH3 being used in the equation below:
N2(g) + 3H2(g)  2NH3
ΔGo =-33.0 kj/mol
ΔG = kj/mol

16. Free Energy and Equilibrium Constant Relationship
At equilibrium, Q = K, and G = 0.
The equation becomes
0 = G + RT lnK
Rearranging, this becomes
G = RT lnK
or,
K = eG/RT

17. What does this mean? ΔGo < 0, K >1 ΔGo > 0, K < 1
More negative ΔGo is, the larger the K value
ΔGo > 0, K < 1
ΔGo = O , K = 1

18. Online Practice Problems
Visit the websites listed. Complete the practice problems on a separate sheet of paper. Check your answers

19. Practice Problem Websites
Entropy
Gibb’s Free Energy
Free Energy and Equilibrium

20. Closure Practice Problems
Chapter 19 in textbook (2015 Edition)
Spontaneous Processes 19.11,19.17
(8th Edition – 19.1, 19.2)
Entropy 19.25, 19.27, 19.41, 19.43, 19.47, 19.53, 19.54
(8th Edition – 19.25, 19.27, 19.29, 19.31, 19.33)

21. Closure Practice Problems Cont
Gibb’s Free Energy
19.57, 19.59,19.60, 19.61, 19.69
8th edition – 19.49, 19.51, 19.53, 19.54, 19.56, 19.58, 19.63, 19.66)
Free energy and equilibrium
19.79, 19.81, 19.83
8th edition – 19,71, 19.76, 19.79
Additional Exercises
8th edition – 19.82, 19.87, 19.88, 19.89, 19.90, 19.92