(a). An endothermic reaction A--B proceeds to completion. Predict the signs of deltaS.

(b). What will be the sign of deltaS for the reaction : N₂(g)+O₂(g)--2 NO(g)

For endothermic reaction, ∆H is positive. So an endothermic reaction can proceed by decreasing its Gibbs energy, if ∆H - T∆S is negative, which is possible only if ∆S is positive.

(b) Formation of nitric oxide from nitrogen and oxygen is an endothermic reaction with ∆H = 90.29 kJ mol¹, and so the entropy change will be positive. The reaction is made spontaneous at very high temperature using electrical arc.