Question

This is the equation for the dissociation of ammonia gas at 293 K. Delta.H = 145 kJ and Delta.S = 195 J/k.

2NH3(g) Right arrow. N2(g) + 3H2(g)

Which correctly states the Delta.G for this dissociation and whether the process is spontaneous or nonspontaneous? Use Delta.G = Delta.H – TDelta.S.
–87.87 kJ, spontaneous
–50 kJ, spontaneous
87.9 kJ, nonspontaneous
202.14 kJ, nonspontaneous

Answer 1

Convert ΔS to kJ/K: 195 J/K = 0.195 kJ/K.
TΔS = 293 K × 0.195 kJ/K = 57.135 kJ.
ΔG = ΔH − TΔS = 145 kJ − 57.135 kJ = +87.87 kJ.

Positive ΔG → nonspontaneous. So: 87.9 kJ, nonspontaneous.