The word entropy is sometimes confused with energy. Although they are related quantities, they are distinct. As described in previous sections, energy measures the capability of an object or system to do work.Entropy, on the other hand, is a measure of the "disorder" of a system. What "disorder refers to is really the number of different microscopic states a system can be in, given that the system has a particular fixed composition, volume, energy, pressure, and temperature. By "microscopic states", we mean the exact states of all the molecules making up the system.