# AP Chemistry Unit 9.5 Free Energy and Equilibrium

Free Energy and Equilibrium

Free Energy at Nonstandard Conditions

• Enthalpy does not depend on volume or pressure, but entropy does
• Positional probability:
• A decreasing ΔG means that the favorability of the forward reaction is increasing (reaction shifts right)
• An increasing ΔG means that the favorability of the forward reaction is decreasing (reaction shifts left)
• R = gas constant → in thermodynamic calculations use the units with Joules (8.314)
• ΔG°: free energy change for the reaction at standard conditions
• Remember that K is the equilibrium constant

Equilibrium and Favorability

 Value of ΔG° +ΔG° ΔG° = 0 ΔG° = – Value of K K < 1 K = 1 K > 1 Value of ΔH° & TΔS° ΔH° > TΔS° ΔH° = TΔS° ΔH° < TΔS°
• Justify if a reaction is spontaneous: refer to equation and explain if ΔG° will be more negative or more positive

Free Energy and Work

• The maximum amount of useful work obtainable from a process at constant temp and pressure equals the change in free energy (energy “free” to do work)

Calculations with Entropy and Enthalpy

• Find Entropy of heat of vaporization: HV (J) / BP (K)
• Find Entropy for vaporization: + ΔH (J) / BP (K);              Find Entropy for condensation: – ΔH (J) / BP (K)
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