This piston is being brought out, so we expect 0 the work to be negative, negative. And we start o V2 ut with zero volume. We end up with a volume p2 of V2, and the external pressure is constant to p2.

所以我们可以想象功是负的,开始的时候体积是,最终的容积是,外界的压力恒为。

麻省理工公开课 - 热力学与动力学课程节选

The property is the limit as p goes to zero of pressure times molar volume.

与摩尔体积的乘积,在气体压强p趋于0时的极限。

麻省理工公开课 - 热力学与动力学课程节选