In multi-specie systems the calculation of Cp and Cv is relatively expensive due
to the cost of mixing the coefficients of the specie thermo model, e.g. JANAF,
and it is significantly more efficient if these are calculated at the same time
as the rest of the thermo-physical properties following the energy solution.
Also the need for CpByCpv is also avoided by the specie thermo providing the
energy type in the form of a boolean 'enthalpy()' function which returns true if
the energy type is an enthalpy form.
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