It is taking place inside this thing, and it's a constant pressure, and we'll do it reversibly, right. So that's what we've got.

它是绝热的，在这个内反应,是在恒压下，它是可逆的，对吧？

麻省理工公开课 - 热力学与动力学课程节选

OK, we're going to do this reversibly, which means we're going to slowly change the external pressure very, very slightly at a time, so that at every point we're basically in equilibrium, p2/ until the pressure reaches a new smaller pressure p2.

整个过程保持可逆，外界压强,变化得很慢，每一个瞬间,都保持平衡，直到压强减小到末态值。

麻省理工公开课 - 热力学与动力学课程节选