"Now notice that as I said, enthalpy is like "total energy". This is why u and h are often times equal for incompressible liquids and solids. The specific volume of an in-compressible liquid or solid is VERY tiny so when you are calculating Pv you will get a very small number even if the pressure is large, simply because the specific volume is so tiny. Gases on the other hand have larger specific volumes, which is why enthalpy and internal energy are not always the same."