Explain entropy and spontaneity of the process.

Explanation

(1) The spontaneous process results in disorders, hence increase in
entropy `(triangle S gt 0)`.
(2) The spontaneous process takes place with the decrease in free
energy `(triangle G lt 0)`.
(3) There are sone spontaneous processes which take place with a
decrease in entropy. For example. neutralisation reaction,
`H_((aq))^(+)+OH_((aq))^(_) rarr H_(2)O_((1)) triangle S lt0`
(4) From second law of thermodynamics, the entropy of the system
and its surropundings increases in the spontaneous process.
`therefore triangle S_("total") = triangle S_("system")+triangleS_("surr")gt0`
(5) To decide the sponntaneity of a process or a reaction it is
essential to consider the entropy of both, the system and the
surroundings.
(6) Hence,
(a) For spontaneous process: `triangle S_("total") = triangle S_("system")+triangleS_("surr")gt0`
(b) For non-spontaneous process : `S_("total") = triangle S_("system")+triangleS_("surr")lt0`
(c) For the process at equilibrium : `triangleS_("total") = triangle S_("system")+triangleS_("surr")=0`