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It takes the right combination of wind,temperature,pressure and humidity to create even a weak tornado.
VOA: special.2010.05.11
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That is, most processes that we're concerned with, they'll happen with something held constant like pressure or temperature or maybe volume.
这句话是说我们所关注的大部分过程，发生的时候都是保持某个量为常数,比如压强，温度或者体积。
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So this unique temperature and unique pressure defines a triple point everywhere, and that's a great reference point.
这样，无论在何处,三相点都具有相同的温度和压强,十分适合来作参考点。
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Mister Harrison had to develop a clock that was not affected by the movement of a ship on the ocean or changes in temperature or atmospheric pressure.
VOA: special.2010.07.14
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We could just collect a bunch of data. For a material .What's the volume it occupies at some pressure and temperature?
对一种物质我们可以得到一系列测量数据,在给定的温度和气压下,它的体积是什么？
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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？
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OK, now what we'd like to do is be able to calculate any of these quantities in terms of temperature, pressure, volume properties.
现在我们想要做的是能够利用,温度，压强和体积的性质,计算上面的物理量。
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On the other hand, temperature, volume and pressure are variables that are much easier in the lab to keep constant.
另一方面，温度，体积和压强,在实验室中比较容易保持恒定。
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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。
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And the equation of state, pressure versus volume at constant temperature, is going to have some form, let's just draw it in there like that.
系统的态函数，恒温下压强比体积，变化曲线，就像这样。
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are all functions of state and parameters that we can control like temperature and pressure.
公式里面的全部都是态函数,我们控制态函数的参数比如温度或者压强。
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Whereas under these conditions, these quantities, if you look at free energy change, for example at constant temperature and pressure, H you can still calculate H.
但是，在这些条件下，这些物理量，如果我们考察自由能的变化,例如在恒定的温度和压强下，我们仍然可以计算。
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Hydrogen gas it's in its most stable state, right at room temperature and pressure.
和常压下氢气是氢元素，最稳定的状态，这个小“0“
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For instance, the pressure and the temperature, or the volume and the pressure.
比如压强和温度，或体积和压强。
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It's a state function, so we're at constant temperature and pressure, and now we want to consider some chemical change or a phase transition or you name it.
这就是态函数，我们处于恒定的温度和压强之下，然后考虑某些化学变化或者相变,或者你想考虑的东西。
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There's a volume, there's a temperature, than the pressure here. There's other volume, temperature and pressure here, corresponding to this system here.
温度等状态函数有本质区别，这个状态有一组，确定的体积，温度与压强。
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And so, again, we see a temperature increase, and we know the work, and the temperature increase, it's a constant pressure thing.
好，我们看到温度升高了，然后我们有做功量和温度的升高量，这是一个恒定压力下的值。
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So, all I want to do now is look at the derivatives of the free energies with respect to temperature and volume and pressure.
我现在所要做的一切就是,考察自由能对,温度，体积和压强的偏导数。
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And I didn't specify the conditions, but if we were to do this under ordinary chemical conditions of some, you'd say room temperature and pressure, right, they all happen spontaneously.
我并没有特别说明反应条件，但是如果我们在通常的化学条件下,实现这些化学反应，比如在室温和大气压下下，他们都是自发的。
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And you can find these compressibility factors in tables. If you want to know the compressibility factors for water, for steam, at a certain pressure and temperature, you go to a table and you find it.
各种气体的压缩系数,想知道水或者水蒸气,在某个温度和压强下的，压缩系数，查表就行了，这是实际气体状态方程的。
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So again with the Gibbs free energy, now I see how to determine, if I change the pressure, if I change the temperature by some modest amount, how much is the Gibbs free energy going to change?
再一次通过吉布斯自由能，我知道当我，适当的改变压强和，温度的时候，吉布斯自由能如何变化？
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Now in this particular reaction, I've got hydrogen gas, iron solid. Those already are elements in their most stable forms at room temperature and pressure.
特定的反应中，我有氢气,固态铁，这些都已经是,处于室温和常压下,最稳定的元素单质。
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And this volume, temperature and pressure doesn't care how you got there. It is what it is.
另一个状态,也有一组确定的体积。
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We know how the volume and temperature vary with respect to each other at constant pressure.
知道在恒定压强下,体积如何随着温度变化。
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Because so much of what we do in chemistry does take place with constant temperature and pressure.
因为化学中我们所做的很多东西,都是在恒定的温度和压强下进行的。
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That is, it's easy to write down straight away that dG with respect to temperature at constant pressure S is minus S.
这就是说，可以很简单的写出dG在,恒定压强下对温度的偏导数,是负。
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You know how pressure changes with temperature at constant volume if you know the equation of state.
如果你知道状态方程,知道在体积恒定的时压强如何随着温度变化。
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There's our condition for equilibrium at constant temperature and pressure.
这就是我们在,恒定温度和压强下的平衡条件。
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You just need a few macroscopic variables that are very familiar to you, like the pressure, the temperature, the volume, the number of moles of each component, the mass of the system.
你只需要某些你非常熟悉的宏观变量,比如压强，温度，体积，每个组分的摩尔数，系统的质量。
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OK, you use the ideal gas law, etc., then you get a relationship that connects the pressure and the temperature, like here we got a relationship that connected the temperatures and the volumes together.
我们会得到，一个联系初末态,的压强和温度的，关系式,就像这个联系过程中。
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