An enthalpy–entropy chart, also known as the H – S chart or Mollier diagram, plots the total heat against entropy, describing the enthalpy of a thermodynamic system. A typical chart covers a pressure range of 0.01–1000 bar, and temperatures up to 800 degrees Celsius. It shows enthalpy H in terms of internal energy U , pressure p and volume V using the relationship H = U + p V (or, in terms of specific enthalpy, specific entropy and specific volume, h = u + p v ).