The standard reaction enthalpy of the reaction: Zn(s) + H₂O(g) ⇌ ZnO(s) + H₂(g) is + 223 kJ/mol and the standard reaction Gibb's functions is +33 kJ mol⁻¹ at 1520 K. Assuming that both ΔH° and ΔS° rem

Question

The standard reaction enthalpy of the reaction: Zn(s) + H₂O(g) ⇌ ZnO(s) + H₂(g) is + 223 kJ/mol and the standard reaction Gibb's functions is +33 kJ mol⁻¹ at 1520 K. Assuming that both ΔH° and ΔS° remain constant, estimate the minimum temperature (in Kelvin) above which the equilibrium constant becomes greater than one.

Prashant Kotian · Accepted Answer

Correct answer: 1784. For the equilibrium constant K to be greater than 1, ΔG° must be less than 0. First, calculate ΔS° using ΔG° = ΔH° - TΔS° at 1520 K: 33 = 223 - 1520 × ΔS° => 1520 × ΔS° = 190 => ΔS° = 190 / 1520 = 0.125 kJ/(K·mol). For ΔG° < 0, T > ΔH° / ΔS° = 223 / 0.125 = 1784 K. Therefore, correct answer is 1784.

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