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Now for this experiment, this is a constant enthalpy experiment for the Joule-Thomson experiment, this is equal to zero.
对于这个实验，焦耳-汤姆逊实验,是一个焓不变的实验,焓变化等于0，所以我可以。
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Even though the signs of the enthalpy changed, and the signs of the entropy changed because it's a combination of the two that matters.
即使自由焓的符号发生变化，熵的符号也会发生变化,因为这两部分都起作用。
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So, I just want to write a few examples down with a few values for delta u or delta H or delta S, and see whether we can get any clues from what we see.
我先写一些例子,例子包含一些内能，自由焓和熵的变化数值，然后看从中,我们能不能得到一些启示。
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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。
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Because eventually they will tell us maybe things about how heat is changing further on.
我们需要知道焓在系统中怎样变化,因为最终它们或许会告诉我们。
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So now we have a different sign for delta H and it still happens spontaneously.
现在自由焓的变化的符号不一样了,但是这个过程仍然自发的进行。
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Do we calculate, you know, delta S, delta u, delta H?
是否要计算熵的变化，内能的变化，自由焓的变化？
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And if I do that then I can find out the change in enthalpy of this reaction. It's just going to be the heat of formation of these three moles of water, minus the heat of formation of the iron oxide. OK.
我就能得到这个,反应的焓的变化,它就是三摩尔水,的生成热，减去氧化铁的,生成热，好。
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H We also saw that dS for constant H and p was greater than zero.
我们同样可以看到如果保持自由焓,和压强不变熵的变化dS也是大于零的。
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pV So there is an arbitrary set point that needs to be defined, right? Because what you actually measure in the lab are changes in enthalpy, just like what you measure when you look at energy change of some sort, you measure the change in energy, right.
焓也是一样，焓是U加,所以需要定义一个任意的设定值,对吧？因为实际上你在实验室里,测得的是焓的改变,就像你在研究某种能量变化时，所测量的那样，你测量的是能量的改变，对吧。
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