Question

The reaction in which carbon and water react to release hydrogen gas has ?H = +31.3 kcal/mol and ?S = +32 cal/(mol•K). What is the value of ?G for the reaction at 300K? What does this value mean?
a) ?G = 21.7 kcal/mol; the reaction is nonspontaneous
b) ?G = -21.7 kcal/mol; the reaction is spontaneous
c) ?G = 2.17 kcal/mol; the reaction is spontaneous at low temperatures only
d) ?G = 21,700 kcal/mol; the reaction is nonspontaneous except under exceptionally high temperature and pressure

Answer 1

The change in the Gibbs free energy of the system that occurs during a reaction is given by-

G = H - TS => 31300cal - 300Kx 32 cal/mol.K=31300 - 9600 = 21700cal=21.7kcal/mol

since (G > 0) unfavourable and non spontaneous & reaction is endrogenic.

so ans. is G = 21.7 kcal/mol; the reaction is nonspontaneous