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They form when the air temperature is about fifteen degrees below zero Celsius.
VOA: special.2010.01.05
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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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They form when the temperature is about five degrees below zero.
VOA: special.2010.01.05
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In principle, this value, this efficiency, can approach 1 as the low temperature approaches absolute zero.
这个值，效率，当低温热源的温度1,是据对零度时可以达到一。
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The temperature often dropped to sixty degrees below zero Celsius.
VOA: special.2009.02.11
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B=0 There's going to be some temperature where B is equal to zero. In that case, your gas is going to look awfully like an ideal gas.
在某个温度,这时，实际气体的表现，十分接近理想气体,高于这一温度它是正的。
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We looked at pressure change before, actually, in discussing the third law, the fact that the entropy goes to zero as the absolute temperature goes to zero for a pure,perfect crystal.
在讨论热力学第三定律的时候，我们讨论过压强变化,即对于纯净的完美晶体,随着温度下降到绝对零度熵也变成零。
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So, this temperature, this absolute zero here, which is absolute zero on the Kelvin scale.
在负无穷处，现在把绝对零度定义为，开尔文温标中的0度。
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Because he thought that would be big enough that in Denmark, the temperature wouldn't go below zero.
因为他觉得这个数字,对于丹麦来说够大了，气温不会低到零度以下。
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So for an ideal gas then, dH/dp under 0 constant temperature, that has to be equal to zero.
所以对于理想气体,偏H偏p在恒温下，等于。
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In other words, T surrounding dS has to be greater than zero, and of course temperature is always positive.
换句话说这就意味着，环境温度T乘以dS必须大于零，当然环境温度T是正的。
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SdT This has minus T dS minus S dT, but the dT part is zero because we're at constant temperature.
这一项包含负的Tds和，但是dT的部分等于零,因为温度为常数。
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So the concept of an absolute zero, a temperature below which you just can't go, that's directly out of the scheme here, this linear interpolation scheme with these two reference points.
这就是绝对零度，这样，从线性插值的图像出发，我们得到了绝对零度的概念，你永远无法达到,低于绝对零度的状态。
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u=0 Constant temperature isothermal delta u is zero.
对等温过程，Δ
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And so now we have this quantity, p times v bar, and the limit of p goes to zero is equal to a constant times the temperature.
不仅仅对氢气或氮气适用，在p趋于0的极限下,它适用于任何气体。
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Now, for an ideal gas, du/dV under =0 constant temperature is equal to zero.
对于理想气体，温度一定,时偏U偏V等于零。
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Because temperature is constant H only 0 cares about temperature. and that's equal to zero.
因为温度是常数，而H只和温度有关,所以这等于0，如果这等于。
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We have an interpolation scheme between zero and 273.16 with two values for this quantity, and we have a linear interpolation that defines our temperature scale, our Kelvin temperature scale.
的两个值做线性插值,就得到了开尔文温标,直线的斜率等于水的三相点,也就是这一点处的f的值,再除以273。16，这是这条直线的斜率，这个量，f在三相点处的值。
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du/dV under constant temperature was equal to zero for an ideal gas. And by analogy, we expect the same thing to be true here, because enthalpy and energy have all this analogy going on here. So let's look at an ideal gas.
偏U偏V在恒温下等于零,可以类比，我们希望在这里也一样，因为焓和能量有很强的类比性，让我们看看理想气体,【理想气体】
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Last time we reach the third law which is telling us that we can't quite get to zero degrees Kelvin .but that as the temperature approaches zero degrees Kelvin, the absolute entropy of a pure substance in perfect crystalline form is zero.
上次课我们得到了热力学第三定律,这个定律告诉我们我们无法,达到0K的温度,但是在我们接近绝对零度的过程中，以完美晶体形式存在的纯物质的绝对熵,也趋向于零。
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So in this experiment here, delta p is less than zero. You need to have this whole thing greater than zero. So delta T is less than zero as well. So if you're below the inversion temperature and you do the Joule-Thomson experiment, you're going to end up with something that's colder on this side than that side.
所以在这个实验中，Δp小于零,这全部都大于零,因此ΔT也小于零,所以如果在低于转变,温度的情况下做焦耳-汤姆孙实验,最后的结果是,这边的温度比这边低。
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