How Chemical Work at Constant Pressure?

Chemical Work at Constant Pressure

The ability of a chemical reaction to perform work at a constant pressure is given by the Gibbs energy AG° where K is the equilibrium constant.

ΔG⁰ = – RT 1n (K)

Calculate ΔG° for a reaction which has an equilibrium constant K= 1.8 x 10^-5 at a temperature T = 298 K and R = 8.314 J K^-1 mo1^-1 is the gas constant.

ΔG⁰ = – RT 1n (K)

ΔG⁰ = – (8.314 J K^-1 mol^-1) (298 K) ln (1.8 x 10^-5)

ΔG⁰ = – (8.314 J K^-1 mol^-1) (298 K) (- 10.925) = + 2.7068 x 10⁴ J mol^-1

ΔG⁰ = + 27.1 K J mol^-1

Note that we normally quote results in multiples of 10³ or 10³ and use the appropriate multiple symbol, here it is kilo with the symbol k. The equilibrium constant K is quoted to two significant figures and a variation in K of ± 0.1 x 10^-5 gives ΔG⁰ with ≈ 0.14 K J mo1^-5 hence the above final result.