Question

For a given reaction, ΔH=78.7kJ/mol, and the reaction is spontaneous at temperatures above the crossover temperature, 461K. The value of ΔS= _______ J/mol⋅K, assuming that ΔH and ΔS do not vary with temperature.

Answer 1

171 J/mol.K

Step-by-step explanation:

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

ΔG = ΔH - T.ΔS

where,

T is the absolute temperature

If ΔG < 0,

ΔH - T.ΔS < 0

ΔH < T.ΔS

ΔS > ΔH/T = (78.7 × 10³ J/mol)/461 K = 171 J/mol.K

ΔS must be at least 171 J/mol.K for the reaction to be spontaneous above 461 K.