Question

For the reaction:

2A(g) + B(g) → 2D(g)

ΔU^Θ = -10.5 kJ and Δs^Θ = -44.1 JK^-1

Calculate ΔG^Θ for the reaction, and predict whether the reaction may occur spontaneously.

Answer 1

ΔH^Θ = ΔU^Θ + Δ^ngRT

ΔU^Θ = -10.5 Kg, Δ^ng = 2 - 3 = -1 mol

R = 8.314 x 10^-3 kJ K^-1 mol^-1

T = 298 K

Hence ΔH^Θ = (-10.5 kJ) + [(-1 mol) x (8.314 x 10^-3 kJ K^-1 mol^-1) x (298 K)]

= -10.5 kJ - 2.478 kJ = -12.978 kJ

According to Gibbs Helmholtz equation:

ΔG^Θ = ΔH^Θ - TΔ^Θ

ΔG^Θ = -12.978 + 13.112 = +0.134 kJ

Since ΔG^Θ is positive, the reaction is non-spontaneous in nature.