19-6 Free Energy Change and Equilibrium

1. 19-6 Free Energy Change and Equilibrium

2. Free Energy Change and Equilibrium Condensation Equilibrium Vaporization

3. Relationship of ΔG° to ΔG for Non-standard Conditions 2 N2(g) + 3 H2(g) 2 NH3(g) ΔG = ΔH - TΔS ΔG° = ΔH° - TΔS° For ideal gases ΔH = ΔH° ΔG = ΔH° - TΔS

4. qrev Vf = R ln ΔS = T Vi Pf Pi Vf = R ln = -R ln = R ln ΔS = Sf – Si Pi Pf Vi P P - R ln - R ln = S° - R ln P = S° S = S° 1 P° Relationship Between S and S° Vf qrev = -w = RT ln Vi

5. 3 PN2PH2 ΔSrxn = 2 SNH3 – SN2 –3SH2+ Rln 2 PNH3 3 PN2PH2 ΔSrxn = ΔS°rxn + Rln 2 PNH3 N2(g) + 3 H2(g) 2 NH3(g) SN2= SN2 – Rln PN2 SH2 =SH2 – Rln PH2 SNH3 = SNH3 – Rln PNH3 ΔSrxn = 2(SNH3 – Rln PNH3) – (SN2 – Rln PN2) –3(SH2 – Rln PH2)

6. 3 2 PN2PH2 ΔG = ΔH° - TΔS°rxn – TR ln 2 PNH3 2 PNH3 ΔG = ΔG° + RT ln 3 2 PN2PH2 3 2 PN2PH2 ΔSrxn = ΔS°rxn + Rln 2 PNH3 ΔG Under Non-standard Conditions ΔG = ΔH° - TΔS ΔG = ΔG° + RT ln Q

7. If the reaction is at equilibrium then: ΔG = ΔG° + RT ln Keq= 0 ΔG and the Equilibrium Constant Keq ΔG = ΔG° + RT ln Q ΔG° = -RT ln Keq

8. Criteria for Spontaneous Change Every chemical reaction consists of both a forward and a reverse reaction. The direction of spontaneous change is the direction in which the free energy decreases.

9. Significance of the Magnitude of ΔG

10. -ΔG° -ΔH° TΔS° ln Keq = = + RT RT RT -ΔH° ΔS° ln Keq = + RT R 19-7 ΔG° and Keq as Functions of Temperature ΔG° = ΔH° -TΔS° ΔG° = -RT ln Keq

11. Van’t Hoff Equation If we evaluate this equation for a change in temperature: Keq2 -ΔH° ΔS° -ΔH° ΔS° - ln = + + RT2 R RT1 R Keq1 Keq2 1 1 -ΔH° - = ln T2 T1 R Keq1

13. -ΔH° slope = R -ΔH° ΔS° ln Keq = + RT R Temperature Dependence of Keq Assume ΔH° and ΔS° do not vary significantly with temperature. -ΔH° = Rslope = -8.3145 J mol-1 K-1  2.2104 K = -1.8102 kJ mol-1