# Exact vs. Inexact Differentials

## Exact

:You should recall, from the previous chapter, that enthalpy is a property or state variable and its differential is therefore exact: dH. The process path that connects states 1 and 2 in no way affects the enthalpy change from state 1 to state 2.

## Inexact

:
In this lesson, we have learned that

#### work

is a#### path variable

and its differential is#### inexact

. We cannot evaluate#### work

without knowing exactly how P and V changed during the process so that we can evaluate the area under the process path on the P-V Diagram.
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