Gibbs Free Energy and Partial Pressure

Question

1. The following reaction is at equilibrium 

 H₂(g) + CO₂(g) ⇔ H₂O(g) + CO(g)

a. Determine the free energy change, ΔG°, at T = 298 K. 

b. If the partial pressures of H₂(g), CO₂(g), H₂O(g), and CO(g) are 20, 40, 0.04, and 0.02 atm, 

respectively, determine the free energy change as a function of temperature, ΔG°(T).

Answer 1

1) The ΔG⁰_rxn = ΔG⁰_f,H2O ⁺ ΔG⁰_f,CO - ΔG⁰_f,CO2 (H₂ has a value of 0) (Look the delta Gs of formation up in thermodynamic table in every Chemistry textbook)

2) ΔG = ΔG⁰ + RTlnQ where R is the gas const 8.314 J/MoleK, T is given in K, and Q is the K expression with the initial conditions subbed in for

Q = P_H2OP_CO/(P_H2P_CO2)

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