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Chem_215_Lect_22_Color

# Chem_215_Lect_22_Color - Dependence of Free Energy on...

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1 Dependence of Free Energy on Pressure Consider the hypothetical reaction aA(g) +bB(g) cC(g) + dD(g) quotient reaction the is Q where Q, ln RT Δ G P P P P ln RT Δ G Δ G o b B a A d D c C o + = + = If Δ G<0, reaction proceeds to right If Δ G=0, reaction is at equilibrium Haber Process: N 2 (g) + 3H 2 (g) 2NH 3 (g) Δ G o = -33.3 kJ a) Is reaction spontaneous under standard conditions? b) Is reaction spontaneous if T increased to 200 o C (473K)? c) Is reaction spontaneous at 25 o C with PNH 3 = 1.00 atm, P N2 = 1.47 atm, and P H2 = 1.00 x 10 -2 atm? Yes No At eq’m

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2 Free Energy and the Equilibrium Constant, K eq Δ G = Δ G o + RT lnQ At equilibrium: Δ G = 0 and Q = K 0 = Δ G o + RT lnK Δ G o = - RT lnK We can calculate K from Δ G o and vice versa
3 Measurement of the temperature dependence of K P Plot ln K P vs 1/T: Slope = - Δ H o /R Intercept = Δ S o /R Δ G o = - RT lnK P R Δ S RT Δ H - K ln Δ S T - Δ H Δ G K ln RT o o P o o o P + = = =

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4 Equilibrium, Free Energy and Extent of Reaction Δ G o = - RT lnK Small Δ G o K 1
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