If you have a quantity which is constant over any closed path, that quantity is a thermodynamics state function.

如果有一个物理量,对任何闭合回路积分是常数，这个物理量就是一个热力学态函数。

麻省理工公开课 - 热力学与动力学课程节选

Then we can take the derivative of that quantity, when we vary the temperature, holding the volume constant.

即恒定体积，改变温度，这里恒定温度下。

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And that implies that since the quantity we want is given by this quantity, which is zero times a constant, the quantity we want is also zero.

因为我们需要的量,是由这个量乘以一个常数，因为这个量是零，因此我们需要的量也是零。

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We discovered that the quantity dA, under conditions of constant volume and temperature, dA TS And A is u minus TS.

我们发现在恒定的体积和温度下，亥姆赫兹自由能的变化，小于零，is，less，than，zero。,亥姆赫兹自由能A等于内能u减去。

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And so now we have this quantity, p times v bar, and the limit of p goes to zero is equal to a constant times the temperature.

不仅仅对氢气或氮气适用，在p趋于0的极限下,它适用于任何气体。

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