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So, these on-changing properties that describe the state of the equilibrium state of the system are called state variables.
这些描述,系统平衡态的,变化的属性,就叫做状态变量。
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Thermodynamicstalks about equilibrium systems and how to go from one state of equilibrium to another state of equilibrium.
热力学研究的是平衡系统,以及如何,从一个平衡态转变到另一个平衡态。
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OK, so now let's try to formulate how to describe the equilibrium state and what dictates spontaneity.
现在我们尝试,找出如何描述平衡态以及,什么东西表明自发性。
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The equilibrium state is the one, and it's just one, in which there are no spontaneous changes that can take place to any other state.
平衡态是一个，而且仅仅是一个态，这个态不会发生自发变化,变成其他的态。
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So the state variables describe the equilibrium's state and they don't care about how this state got to where it is.
状态变量,描述平衡态，它们并不关心,系统是如何演化成这样的。
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The whole thing's going to come to some new equilibrium temperature between the products and the oil or whatever's around it, and we're going to measure that.
生成物和周围的油或,别的什么东西之间,达到某种新的平衡态，我们要测量的就是这个。
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And the cause of some thermodynamics have even been applied to economics, systems out of equilibrium, like big companies like Enron, you know, completely out of equilibrium, crash and burn.
热力学中的一些观点,甚至被应用到经济学中，非平衡态系统，比如像安永那样大公司,彻底偏离平衡态,最后破产了。
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In the case here, tha t I just illustrated with the little cart going down the valley, would be exactly the same with regular energy, the equilibrium state is one of lowest energy, right.
在现在所考虑的情况下,我刚才所描述的小车沿着山谷下行，结论会像能量判据一样，平衡态是能量最低的态。
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If you have the number of moles and two intensive variables, then you know everything there is to know about the system.
如果你有摩尔数,和两个强度量，你就能知道关于这个系统的一切,关于系统的平衡态的一切。
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I could have that path be very slow and steady, so that at every point along the way, my gas is an equilibrium.
我可以很慢，很稳定地经过这条路径，因此在这条路径上的任意一点，气体都处于平衡态。
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Now we want to show a notation, how do we go from one equilibrium state like this describes to another equilibrium state?
现在我们要展示一种记号，来标记）我们如何,从这里描述的,这样的一个平衡态过渡到另一个平衡态？
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That is, the chain, they could they could be approached with very little change from the equilibrium state.
这些态可以,通过平衡态,发生一些微小的变化得到。
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For instance, you want to know how much energy you're going toget out from doing this expansion.
比如，你想知道在这个膨胀过程中,到另一个平衡态的路径。
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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 now, what is this saying, the equilibrium state is the one with the lowest possible enthalpy.
这时，上面的结论表明,平衡态是自由焓最小的态。
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I've gone from 1 equilibrium state to another equilibrium state and the equal sign means you go from this state to that state.
从一个平衡态,过渡到了另一个平衡态,等号表示,从这个态到了那个态。
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We're going to find other properties that do care about the history of the system like work, that you put in the system, or heat that you put in the system, or some other variables But you can't use those to define the equilibrium state.
我们还会发现其他一些,与系统的历史有关的性质,比如你对系统做的功，或者你向系统传递的热量，或其他的变量,但你不能用它们,来定义平衡态。
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and added a structure of math upon it, to build this edifice, which is a very solid edifice of thermodynamics as a science of equilibrium systems.
了这座热力学的坚固大厦，这是一门，平衡态系统,的科学。
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And knowing now how to calculate these free energies especially the Helmholtz and the Gibbs free energies,that's what's going to guide us in really calculating quantitatively, OK, where will equilibrium lie.
知道如何计算,这些自由能,尤其是亥姆赫兹和吉布斯自由能之后,这些数值计算就能告诉我们，平衡态到底是什么样子。
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But if the system is in equilibrium, none of those states has lower enthalpy.
但是如果系统处于平衡态，所有其他的态都不可能具有更低的自由焓。
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So it applies to macroscopic systems that are in equilibrium, and how to go from one equilibrium state to another equilibrium state, and it's entirely empirical in its foundation.
因此，热力学研究的是平衡态的宏观系统,以及如何从,一个平衡态过渡到另一个平衡态，它完全是建立在经验的基础上的。
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So, we take our two equilibrium states, and you just put an equal sign between them, and the equal sign means go from one to the other.
我们写出两个平衡态，然后你只需要在它们之间放一个等号，等号表示,从一个过渡到另一个。
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We can go back and forth between these two equilibrium states They're connected.
我们可以,在这两个平衡态间往返,它们是相互联系的。
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Well, the equilibrium state is the one with the gases completely mixed.
平衡态就是,气体完全混合的态。
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You could take a continuous path, where you have an infinite equilibrium points in between the two, a smooth path, whereyoudrop pressureand temperature simultaneosly in little increments.
你可以选择光滑的连续路径，在初末态间有,无数个平衡态的点，压强和温度同时一点,一点地下降。
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Of course there are lots of states that would have maybe local pockets of one substance in excess and another substance in excess somewhere else In other words, there would be lots of states nearby to the equilibrium state.
当然，我们有很多的态,这些态中，某些位置被一种气体完全占据,另外一些位置被另一种气体完全占据,换句话说,在平衡态附近有很多的态。
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If it equals zero, then we're at equilibrium.
如果公式等于零，那么系统就处于平衡态。
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To figure out equilibrium. And what the conditions were.
平衡态和平衡条件。
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So the point is, once you're at equilibrium none of the other states they're accessible, the system could rearrange itself to form them, but there is no accessible state that has higher entropy than the equilibrium state.
所以要点在于，如果你处于平衡态,其他所有的态都无法达到，我们可以重组体统来形成这些态，但没有一个可以达到的态,有比平衡态大的熵。
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OK, we're going to do this reversibly, which means we're going to slowly change the external pressure very, very slightly at a time, so that at every point we're basically in equilibrium, p2/ until the pressure reaches a new smaller pressure p2.
整个过程保持可逆，外界压强,变化得很慢，每一个瞬间,都保持平衡，直到压强减小到末态值。
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