Spontaneous wants to go forward on its own K > Q or > 0 or < 0 ∆Suniverse ∆Gsystem Non-spontaneous wants to go backward on its own K < Q or < 0 or > 0 ∆Suniverse ∆Gsystem Equilibrium doesn’t prefer one direction over the other K = Q or = 0 or = 0 ∆Suniverse ∆Gsystem = TΔS = TΔS° = + RTlnQ ΔG ΔH – ΔG° ΔH° – ΔG ΔG° (ΔG° = when Q = 1 or standard conditions) ΔG Temperature ΔH ΔS ΔG Equilibrium Considerations < 0 > 0 Spontaneous at all ΔH ΔS Always Negative Not possible negative positive temperatures > 0 < 0 Spontaneous at any ΔH ΔS Always Positive Not possible positive negative temperature < 0 < 0 Can be positive or negative Spontaneous at ΔH ΔS “low” T = negative negative depending on T temperatures T < > 0 > 0 Can be positive or negative Spontaneous at ΔH ΔS “high” T = positive positive depending on T temperatures T > verses Keq: ΔG° K = or ΔG° tells you where the equilibrium lies ΔG° = –RTlnKeq If < 0 the equilibrium favors the products Keq > 1 (because Q = 1 at standard conditions) ΔG° If > 0 the equilibrium favors the reactants Keq < 1 (because Q = 1 at standard conditions) ΔG° (note if it’s not at standard conditions Q can equal anything so will only tell you the ΔG relationship between K and Q when < 0 the K > Q and vice versa) – ΔG
Spontaneous wants to go forward on its own K > Q or ∆Suniverse > 0 or ∆Gsystem < 0 Non-spontaneous wants to go backward on its own K < Q or ∆Suniverse < 0 or ∆Gsystem > 0 Equilibrium doesn’t prefer one direction over the other K = Q or ∆Suniverse = 0 or ∆Gsystem = 0 ΔG = ΔH – TΔS ΔG° = ΔH° – TΔS° ΔG = ΔG° + RTlnQ (ΔG° = ΔG when Q = 1 or standard conditions) ΔH ΔS ΔG Temperature Considerations Equilibrium ΔH < 0 negative ΔS > 0 positive Always Negative Spontaneous at all temperatures Not possible ΔH > 0 positive ΔS < 0 negative Always Positive Spontaneous at any temperature Not possible ΔH < 0 negative ΔS < 0 negative Can be positive or negative depending on T Spontaneous at “low” temperatures T < T = ΔH > 0 positive ΔS > 0 positive Can be positive or negative depending on T Spontaneous at “high” temperatures T > T = ΔG° verses Keq: ΔG° tells you where the equilibrium lies K = or ΔG° = –RTlnKeq If ΔG° < 0 the equilibrium favors the products Keq > 1 (because Q = 1 at standard conditions) If ΔG° > 0 the equilibrium favors the reactants Keq < 1 (because Q = 1 at standard conditions) (note if it’s not at standard conditions Q can equal anything so ΔG will only tell you the relationship between K and Q – when ΔG < 0 the K > Q and vice versa)
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