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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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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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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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Now let's change the pressure and temperature and sweep through a whole range of pressures and temperatures and measure the volume in every one of them.
然后改变气压和温度,并且让气压和温度,取便所有可能的数值,测量相应的体积。
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This is very different from the functions of state like pressure and temperature.
联系初末两态的整个过程,这与压强。
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In this case, V = /P. Have two quantities and the number of moles gives you another property. You don't need to know the volume. All you need to know is the pressure and temperature and the number of moles to get the volume.
以及气体的摩尔数,就可以得到第三个量,知道压强，温度和气体的,摩尔数就可以推导出气体的体积,这称为状态方程,它建立了状态函数之间的联系。
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Pressure and temperature, right.
老师：压强和温度对。
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STUDENT: Pressure and temperature.
学生：压强和温度。
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In other words, the order of taking the derivatives with respect to pressure and temperature doesn't matter And what this will show is that dS/dp dS/dp at constant temperature, here we saw how entropy varies with volume, this is going to show us how it varies with pressure.
换句话说,对温度和压强的求导顺序无关紧要,结果会表明,恒定温度下的，对应我们上面看到的，熵如何随着体积变化，这个式子告诉我们，熵如何随着压强变化。
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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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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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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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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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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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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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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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Similarly for G as a function of temperature and pressure, I can go through the same procedure.
同样的G作为,温度和压强的函数，我可以采用相同的步骤。
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