Because if it's irreversible, it's very likely that I don't know what the pressure inside the system is doing while this is happening.

因为对不可逆过程，系统内部的压强,没有明确的定义,气体不处于平衡态。

麻省理工公开课 - 热力学与动力学课程节选

The energy expanded by the system is smaller for the irreversible process.

它做的,功要小些。

麻省理工公开课 - 热力学与动力学课程节选

Wirr Minus w irreversible, this is the work which is done to the environment by the system, -Wrev minus w irreversible is always smaller than minus w reversible.

一点提示，不可逆过程中系统,对外界做的功，总是小于,之前我们。

麻省理工公开课 - 热力学与动力学课程节选