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.

ingwadlatp 2022-07-20 Answered
Is enthalpy also valid for liquids and solids?
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Answers (1)

Jaylene Tyler
Answered 2022-07-21 Author has 10 answers
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 c
and 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 P
For a solid, dV=0 for a fixed amount of matter, and furthermore d E V d P, thus
H=E
There is nothing wrong in these concepts (the thermodynamic potentials) for liquids and solids.
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