A thermodynamic graphical depiction known as an enthalpy-entropy (H-S) diagram depicts changes in a substance's enthalpy (H) and entropy (S) while it goes through a physical or chemical transition. The vertical axis shows the enthalpy, which is the heat content of the system under constant pressure, and the horizontal axis represents entropy, which is a measure of the degree of disorder or unpredictability of a system.

Phase changes, chemical reactions, and heat transmission are just a few examples of the different thermodynamic processes that may be studied and understood using the H-S diagram. The efficiency of energy conversion procedures like power cycles and refrigeration cycles may also be ascertained using the diagram.