Most literatures on thermodynamics are written or started with the language of 'ideal gas'.
This confuses me a lot when I switch to consider solids. For example, the enthalpy of a system
is defined as H = U + P*V, where P is the pressure of the 'system'. This definition is found to be convenient
when dealing with gas. But in terms of solids, I really doubt if the 'pressure' is meaningful. The volume makes
sense but its relation with energy should be expressed in another way when we consider for example cold-