But we've defined the enthalpy of those elements in their stable state at room temperature and pressure as zero, right?

但我们已经定义了这些,元素处于它们室温和常压下,最稳定的状态时的焓为零，对吧？

麻省理工公开课 - 热力学与动力学课程节选

What we define as zero is the enthalpy of every element in its natural state at room temperature and ambient pressure.

我们将零点定义为每种元素,在室温和正常大气压下,在其自然状态下的焓。

麻省理工公开课 - 热力学与动力学课程节选

This is just an equality. I have a constant pressure dH process. This term here is equal to zero.

这是一个等式，这是个恒压过程,这项等于零，这意味着。

麻省理工公开课 - 热力学与动力学课程节选

We looked at pressure change before, actually, in discussing the third law, the fact that the entropy goes to zero as the absolute temperature goes to zero for a pure,perfect crystal.

在讨论热力学第三定律的时候，我们讨论过压强变化,即对于纯净的完美晶体,随着温度下降到绝对零度熵也变成零。

麻省理工公开课 - 热力学与动力学课程节选

And so now, instead of using these reference points for the Kelvin scale, we use the absolute zero, which isn't going to care what the pressure is.

就像理想气体温标,与气体的种类无关一样，具有普适性，在开尔文温标中。

麻省理工公开课 - 热力学与动力学课程节选

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

And there is no work done on the surroundings because pressure is zero.

这里系统没有对环境做功,因为压强是零。

麻省理工公开课 - 热力学与动力学课程节选

First let's set the external pressure equal to zero.

首先，让外部压强为零。

麻省理工公开课 - 热力学与动力学课程节选

The atoms or molecules in the gas don't know that there are other atoms and molecules in the gas, and then you end up with this universal property. All right, so gases that have this universal property, even when the pressure is not zero, those are the ideal gases.

可以忽略,这样就得到了理想气体的性质,在有限压强下,依然能保持这些性质的气体，被称为理想气体，本课中我们把大部分气体，都作为理想气体来处理。

麻省理工公开课 - 热力学与动力学课程节选

So if delta v is negative, in this case delta v is negative, OK, delta v is negative, pressure is a positive number, negative times negative is positive, work is greater than zero.

也就是当活塞,压缩气体的时候，做的功是正的，按照这一规定,我们需要在这里，加上一个负号，这是习惯规定。

麻省理工公开课 - 热力学与动力学课程节选

Normally I couldn't do that Vdp because this term would have p dV plus V dp, but we've specified the pressure is constant, so the dp part is zero.

一般情况下我不能这么写,因为这一项会包含pdV和，但是我们已经假定压强为常数，所以包含dp的部分等于零。

麻省理工公开课 - 热力学与动力学课程节选

I'm pressing on the gas. So I expect that to be a positive number. The pressure is constant 0 p. The V goes from V1 to zero.

我们对气体加压,所以这应该是一个正数,压强是常数，p，V从V1变成。

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