Question

For the reaction \[\ce{Ag2O_{(s)} -> 2Ag_{(s)} + 1/2O2_{(g)}}\]: ΔH = 30.56 kJ mol⁻¹ and ΔS = 6.66 JK⁻¹ mol⁻¹ (at 1 atm). Calculate the temperature at which ΔG is equal to zero. Also predict the direction of the reaction

1. at this temperature and
2. below this temperature.

Answer 1

Given, ∆H = 30.56 kJ mol⁻¹ = 30560 J mol⁻¹

∆S = 6.66 × 10⁻³ kJ K⁻¹ mol⁻¹

T = ?

at which ∆G = 0

∆G = ∆H – T∆S

0 = ∆H – T∆S

T = `(Δ"H")/(Δ"S")`

T = `(30.56  "kJ mol"^-1)/(6.66  xx 10^-3  "kJ mol"^-1)`

T = 4589 K

1. At 4589K; ∆G = 0 the reaction is in equilibrium.
2. at temperature below 4598 K; ∆H > T∆S
   ∆G = ∆H – T∆S > 0, the reaction in the forward direction, is non spontaneous. In other words the reaction occurs in the backward direction.