Question

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?

Answer 1

Answer:

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.