Entropy is a measure of the disorder of a system. The idea of Entropy comes from the second law of thermodynamics, which states that all systems tend to increase in disorder. The significance of entropy is that when a spontaneous change occurs in a system, a positive value for Entropy will be obtained. Spontaneous changes in an isolated chemical system occur with an increase in entropy. Entropy, like temperature, pressure, and enthalpy, is also a state property and is represented in the literature by the symbol “S”. Like enthalpy, usually the change in Entropy is calculated (ΔS). Enthalpy change, Entropy change, and change in free energy (Gibbs Free Energy) are related. A spontaneous reaction is one that occurs without any outside intervention. Processes that are spontaneous in one direction are non-spontaneous in the reverse direction.