It's related to the heat capacity, the constant volume of heat capacity and something you could measure.

它联系了热能，恒容热容和一些,我们能够测量的物理量。

麻省理工公开课 - 热力学与动力学课程节选

When I flail my arms around I generate work and heat. This is not a constant volume process.

这不是一个恒容过程,但如果我是一个系统，当我做这些的时候。

麻省理工公开课 - 热力学与动力学课程节选

You just change volume to pressure and basically you're looking at enthalpy under a constant -- anything that's done at a constant volume path with energy, there's the same thing happening under constant pressure path for enthalpy.

可以看到这就是把体积换成了压强,一般我们都是在一种恒定状态下,考虑焓的，任何在恒容条件下,能伴随能量变化的东西，也在恒压条件下伴随焓同样地变化,所以你可以经常。

麻省理工公开课 - 热力学与动力学课程节选

It's not constant pressure, because we have a delta p going on. It's not constant volume either.

也不是恒容，这个限制,是这个实验的限制。

麻省理工公开课 - 热力学与动力学课程节选

v du/dV under constant temperature. du/dT v under constant volume. You use the Joule expansion to find these quantities.

像偏u偏v，恒温下的偏u偏,恒容下的偏u偏,你们知道怎么运用焦耳定律。

麻省理工公开课 - 热力学与动力学课程节选

Over here, we have dq=Cp dT, the heat, the proportionality between heat - and temperature rise is given by this, the constant pressure heat capacity.

这里我有dq=CpdT，这是热量，这是联系热量,和温度变化的系数，恒压热容。

麻省理工公开课 - 热力学与动力学课程节选

If you have a real gas and you write du is Cv dT and your path is not a constant volume path, then you are making a mistake. But for an ideal gas, you can always write this. And this turns out to be very useful to remember.

对于真实气体，如果其变化过程,不是恒容的，du=Cv*dT就不成立，但对于理想气体,这条规则永远成立,这一点非常有用，请记住。

麻省理工公开课 - 热力学与动力学课程节选