Hydrogen sulfide decomposes according to the following reaction, 2 H2S (g) → 2 H2 (g) + S2 (g) where ∆S = + 78.1 J/K, ∆H = + 169.4 kJ, which answer describes the entire range of temperatures where the reaction would be spontaneous?

Question

Humberto Osborn

Chemistry

12 October, 16:26

Hydrogen sulfide decomposes according to the following reaction, 2 H2S (g) → 2 H2 (g) + S2 (g) where ∆S = + 78.1 J/K, ∆H = + 169.4 kJ, which answer describes the entire range of temperatures where the reaction would be spontaneous?

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Answers (1)

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Heath Carey · Answer 1

The reaction is spontaneous when T > 2170 K.

Explanation:

The spontaneity of a reaction is related to the standard Gibbs free energy (ΔG°). When ΔG° < 0 the reaction is spontaneous. ΔG° is related to the standard enthalpy (ΔH°) and the standard entropy (ΔS°) through the following expression:

ΔG° = ΔH° - T.ΔS°

where,

T is the absolute temperature

The reaction is spontaneous when ΔG° < 0, that is,

ΔH° - T.ΔS° < 0

ΔH° < T.ΔS°

T > ΔH°/ΔS° = (169.4 * 10³ J) / (78.1 J/K) = 2170 K

The reaction is spontaneous when T > 2170 K.