# How is change in entropy of universe related to the energy released by system that can be used to do work?

What does change in entropy ($\Delta S$) represent ? How does change in entropy of a universe ($\Delta S_{univ}$) give us information about energy available to do work.

I would like to know the physical significance of entropy of universe and how it is related to energy energy released by system that can be used to do work (Not in terms of equation. I would want to know its physical significance).

Suppose you are a magician & want to make a rabbit having internal energy $U$. so, in order to invoke the rabbit, you have to supply $U$. But wait! In order to make the rabbit, you not only have to provide $U$ but also the energy necessary to create space for the rabbit by asiding the atmosphere. So, the total energy you supply is $U + PV$. This is enthalpy. But again wait! You don't have to supply the entire $U + PV$ as there is an associated entropy with the formation of the rabbit i.e. $S$ i.e. the energy supplied by you, the Great Magician is $U + PV - T S$. This is the free energy as it is the only energy you will get after vanishing the rabbit.