Question

in physical significance of entropy,it is written that entropy as unavailable energy. what is anavailable energy? i do not make out this

Answer 1

The energy associated with a chemical reaction can be used to do work. The free energy of a system is the sum of its enthalpy (H) minus the product of the temperature (Kelvin) and the entropy (S) of the system

G = H - TS

Here G denotes gibbs free energy and when it is divide it with number of moles, gibbs free energy per moles is obtain which donates the useful work done.

It is the maximum amount of available energy which can be converted in to work. Since entropy is the only energy which is not convertible into work. Therefore it is known as unavailable energy.