Is enthalpy also valid for liquids and solids?

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Jaylene Tyler · Accepted Answer

For solids, as well as for liquids and gases, you can define a specific heat as      c    V    ≡            (                        ∂          U                          ∂          T                    )        V  and      c    P    ≡            (                        ∂          U                          ∂          T                    )        P  For solids, however,  V is basically a constant, so that with excellent approximation      c    P    ≈      c    V    ≡  cand we can now define an internal energy E as  d  E  =  c  (  T  )  d  T    .We can proceed likewise with enthalpy:  d  H  =  d  E  +  d  (  P  V  )  =  c  (  T  )  d  T  +  P  d  V  +  V  d  PFor a solid, dV=0 for a fixed amount of matter, and furthermore   d  E  ≫  V  d  P, thusH=EThere is nothing wrong in these concepts (the thermodynamic potentials) for liquids and solids.

The definition of enthalpy is H=E+PV, is it only valid for (ideal) gas? As this naturally comes from the first law of thermodynamics, dE=dQ+PdV for a enclosed system of gas.

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