Clausius Inequality

Theorem

In a cyclic process, the following equation holds.

$\oint {{\delta Q} \over {T}} \le 0$

Especially, if the process is reversible, the following is true.

$\oint {{\delta Q_{\text{rev}}} \over {T}} = 0$

Explanation

$20180731\_182816.png$

A cyclic process refers to a process in which the state of the system at the beginning and the end of the process is the same. If the entire process is reversible, its closed integral is always $0$ , and then, $Q := Q_{\text{rev}}$ is used.