物理化学

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• A reversible change in thermodynamics is a change that can be reversed by an infinitesimal modification of a variable. The key word 'infinitesimal' sharpens the everyday meaning of the word 'reversible' as something that can change direction. We say that a system is in equilibrium with its surroundings if an infinitesimal change in the conditions in opposite directions results in opposite changes in its state. (查看原文)

  [已注销] 2 回复 1赞 2011-02-12 20:05:58

• Intermolecular forces are so important when the temperature is so low that the molecules travel with such low mean speed that can be captrued by one another. At low pressures, when the sample occupies a large volume, the molecular are so far apart for most of the time that the intermolecular forces plya no significant role, and the gas behaves virtually perfectly. At moderate pressures, when the average separation of the moleculer is only a few molecular diameters, the attractive forces dominate the repulsive forces. In this case, the gas can be expected to be more compressible than a perfect gas because the forces help to draw the molecules together. At high pressures, when the average separation of the molecules is small, the repulsive force dominate and the gas can be expected to be les... (查看原文)

  앵도 2012-02-28 09:51:38

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