There's an interplay between the energy inside the gas which is the heat energy which is allowing me to do all that work to be outside, and so I'm using up some of the energy that's inside the gas to do the work on the outside.

即使没有热传递,能量也能以,做功的形式传递出去，气体的一部分内能,转化成了功。

麻省理工公开课 - 热力学与动力学课程节选