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Enthalpy
The analysis in the previous section is based on the premise that
and
are the two independent parameters that specify the system.
Suppose, however, that we choose
and
to be the two independent parameters. Because

(6.90) 
we can rewrite Equation (6.82) in the form

(6.91) 
where

(6.92) 
is termed the enthalpy. The name is derived from the Greek enthalpein, which means to ``to warm in."
The analysis now proceeds in an analogous manner to that in the preceding section. First, we
write

(6.93) 
which implies that

(6.94) 
Comparison of Equations (6.91) and (6.94) yields
We also know that

(6.97) 
or

(6.98) 
Thus, it follows from Equations (6.95) and (6.96) that

(6.99) 
Next: Helmholtz Free Energy
Up: Classical Thermodynamics
Previous: Internal Energy
Richard Fitzpatrick
20160125