7. Free Energy Review: MgO + C(graph)  Mg + CO
∆Ho = KJ/mol ∆So = J/K
a. Is the reaction thermodynamically favorable under standard conditions?
b. Does the temperature have to be increased or decreased to experience a change in ∆G?
c. Enthalpy driven or entropy driven?
d. At what temperature does the reaction experience a change in ∆G?

8. If ∆G is (-) If ∆G is (+) Free Energy and Equilibrium:
Spontaneous definition (again) : Occurs on it’s own, without any outside intervention, in the direction of equilibrium.
The Equilibrium Connection:
If ∆G is (-)
If ∆G is (+)

9. Free Energy and Equilibrium:
There is also a mathematical relationship between spontaneity and equilibrium

10. How is this used:
Determine the ∆Grxn for the formation of 1.0 mole of ammonia from hydrogen and nitrogen gas. Use this value to calculate the equilibrium constant for this reaction at 25oC.
1 2 N H2 ↔ NH ∆Gf for NH3 = KJ/mol
∆Gf for N2 = 0 kJ/mol
∆Gf for H2 = 0 kJ/mol

11. Thermo vs. Kinetics:
Not all spontaneous reactions actually happen “spontaneously”, WHY???
Thermodynamics only tells us if a reaction is theoretically spontaneous,
while the kinetics of a reaction can still prevent it from happening.

12. Thermo vs. Kinetics:
An example of a spontaneous reaction that kinetics stops from happening …
C(diamond)  C(graphite) ∆G = -3 kJ/molrxn
The bonds within diamond are so strong, resulting in such a high activation energy, that the reaction never actually starts!

13. Thermo vs. Kinetics: Extremely high Ea
An example of a spontaneous reaction that kinetics stops from happening …
C(diamond)  C(graphite)

14. Thermo vs. Kinetics:
An example of a spontaneous reaction that kinetics stops from happening …
C(diamond)  C(graphite) ∆G = -3 kJ/molrxn
This reaction is thermodynamically favorable, but kinetically unfavorable.