Question

If a reaction is exothermic does it mean that it is spontaneous? And also, if the reaction is endothermic does it mean that it is non spontaneous? Thanks

Answer 1

the spontaneity of the reaction not only depends upon DH, and also DS. so that a new term is introduced called as change in gibbs free energy (DG).

DG = DH - TDS

If DG = -ve , The process is spontaneous.

if DH = -ve ,DS = +ve , DG = -ve always , The process is spontaneous.

   DH = +ve , DS = -ve , DG = +ve always, The process is non-spontaneous

DH = -ve , DS = -ve , DG = sign depeds on Temperature.

DH = +ve , DS = +ve DG = sign depeds on Temperature.