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OK, important -- if you are part of this group here think about it and make sure you understand that.
好的，这很重要，如果刚才你选了可逆过程,请好好想想并且保证已经理解了这个问题。
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So for the reversible process, the work done is the integral under the pressure volume state function, the function of state.
对可逆过程，做的功,是压强体积态函数曲线下，的积分面积。
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Adiabatic can be either reversible or not, and we're going to do that probably next time or two times.
绝热过程可以是可逆的，也可以不是，我们可能会在下一次或下下次课上,研究这个问题。
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it becomes a gray area but it should be pretty clear if you can treat something is reversible are irreversible.
这是个灰色区域,但什么可以当作可逆过程处理,而什么要当作不可逆过程,这是相当清楚的。
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Because it's so important. And I should add and also under reversible work, where the external pressure is equal to the internal pressure.
而且我还要说应该在外部压强,和内部压强相等的,可逆过程中引入它。
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Wrev w reversible. in this case here let's see this is it's a pressure is going down.
曲线下的面积，可逆过程的功,这个过程中。
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Anybody have any questions on that, because when we voted, the majority of the class thought it was reversible Yes.
上节课我们投票时，多数人都认为它是一个可逆过程，而现在大家应该都知道了,它其实是不可逆过程，有问题吗？
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How many people vote for that this is a reversible process? I've got one vote back there two votes, three votes, four votes. Anybody else?
有多少人认为,这是一个可逆过程？有一个，两个，三个,四个，还有别的人吗？
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So a reversible process leads to requiring certain quantities to be maximized.
因此可逆过程要求,一些物理量要达到最大值。
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get back to the initial point is going to require some input from outside, like heat or extra work or extra heat or something because you've done an irreversible process.
如果要逆转它,回到初始点，就需要外界的投入，比如额外的功，额外的热量等等,因为你进行了一个不可逆过程。
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Maximum work out is by reversible path.
可逆过程产生最大功。
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And all we know about this is that it's really for some irreversible reversible step.
我们知道,这个式子,对不可逆过程成立。
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Because if it's irreversible, it's very likely that I don't know what the pressure inside the system is doing while this is happening.
因为对不可逆过程，系统内部的压强,没有明确的定义,气体不处于平衡态。
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And I want to make sure everybody figured out that it really was an irreversible expansion.
或者多孔塞的,不可逆的等焓过程。
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that instead of all the steps being reversible, let's just put in one irreversible step.
不是所有的过程都是可逆的，其中有一个过程不可逆。
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So w, the work is less for the irreversible process than the reversible process.
不可逆过程中系统对外界,做的功要比可逆过程时小。
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This is equal to zero. So this irreversible process this Joule-Thomson process, is a constant enthalpy process. Delta h for this process is equal to zero.
等于0。所以这个不可逆过程,也就是焦耳-汤姆逊过程,是一个等焓过程。
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All right, let's calculate the work that's involved with these two processes.
这些路径都是可逆的,可逆过程指的。
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we're going to have a difference here between the irreversible case and the reversible one.
可逆过程,和不可逆过程,会有不同。
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So for an irreversible process, I wouldn't really be allowed to put a path there.
不可逆过程，是无法画出路径曲线来的。
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The reversible process is going to be colder because it has to expend more energy.
可逆过程降温更多,因为输出的能量更多。
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I can do that because it's reversible, and I can get a functional form out.
画出路径就意味着过程是可逆的，下面我们来看这条曲线的函数形式。
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It's really important that this, that you remember that this is the reversible case.
一定要记住，整个过程是可逆的。
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You can only do this because it's reversible. What else do I know?
这一步,只对可逆过程成立，还有什么已知条件？
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T2 Is the temperature T2 in this process smaller or larger than if I were to do the process reversibly with the same endpoint pressure.
这里的末态温度,与经过可逆绝热过程,到达相同压强的末态温度相比哪个比较高呢？
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If it was non-reversible, I would be allowed to put an initial point and a final point, but I wouldn't be allowed to put a path between them like this, connecting them together.
如果是不可逆过程，我可以画出过程的初态点,和末态点，但是我不能再像这样,画出连接这两个点的，路径曲线来。
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So the final process involves do it reversibly, or almost reversibly.
最后我们讨论，可逆过程。
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The temperature is not going to cool as much for the irreversible process.
对不可逆过程,降温不会有可逆过程多。
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And again, I want to stress this is a reversible path.
再强调一次，我们研究的是可逆过程。
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That is, this is derived in the case for reversible paths.
即这些都是通过利用可逆过程推导出来的。
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