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  • 蒸气压降压

    Text from 'De Bello Gallico' discussing military strategy and observations.

    What did Caesar say?
    ::凯撒说了什么?

    Latin is an interesting and useful language, even if you don’t want to read Julius Caesar’s writings. A knowledge of Latin helps us understand our own language better. Take the word “colligative.” Where did that come from? If you know a little Latin, you know that it comes from two Latin words meaning “to tie together.” This helps you better understand some of the science terminology we use every day.
    ::拉丁语既有趣又有用,即使你不想读朱利叶斯·凯撒的著作。 拉丁语知识有助于我们更好地了解我们自己的语言。 使用“共性”一词从何而来?如果你懂一点拉丁语,你知道它来自两个拉丁语词,意思是“连结 ” 。 这有助于你更好地了解我们每天使用的一些科学术语。

    Vapor Pressure Lowering
    ::蒸气压降压

    A colligative property is a property of a solution that depends only on the number of solute particles dissolved in the solution and not on their identity. Recall that the of a is determined by how easily its molecules are able to escape the surface of the liquid and enter the gaseous phase . When a liquid evaporates easily, it will have a relatively large number of its molecules in the phase and thus will have a high vapor pressure. Liquids that do not evaporate easily have a lower vapor pressure. Figure shows the surface of a pure solvent compared to a solution. In the picture on the left, the surface is entirely occupied by liquid molecules, some of which will evaporate and form a vapor pressure. On the right, a nonvolatile solute has been dissolved into the solvent. Nonvolatile means that the solute itself has little tendency to evaporate. Because some of the surface is now occupied by solute particles, there is less room for solvent molecules. This results in less solvent being able to evaporate. The addition of a nonvolatile solute results in a lowering of the vapor pressure of the solvent.
    ::共解属性是一种溶液特性的属性,它仅取决于溶液溶解溶液溶解的溶液粒子的数量,而不是其特性。回顾一个分子的表面完全由液体分子占据,有些分子会蒸发并形成蒸发压力。当液体蒸发很容易时,它就会在阶段中拥有数量相对较大的分子,因此会产生高蒸发压。不蒸发的液体很容易蒸发,其蒸发压力较低。图显示的是纯溶剂与溶液相比的表面。在左边的图片中,表面完全由液体分子占据,其中一些分子将蒸发并形成蒸发压力。在右边,溶剂溶液溶解了非挥发性溶液。不挥发性意味着溶液本身几乎没有蒸发倾向。由于某些表面目前被溶液粒子占据,溶剂分子的容度较小。这导致溶剂较不易蒸发。在低的溶剂中添加非挥发性溶剂。

    Comparison of a pure solvent's surface and a solution with nonvolatile solute affecting vapor pressure.

    The solution on the right left has had some of its solvent particles replaced by solute particles. Since the solute particles do not evaporate, the vapor pressure of the solution is lower than that of the pure solvent.
    ::左边的溶液中有一些溶剂粒子被溶液粒子所取代。 由于溶液粒子不蒸发,溶液的蒸气压力比纯溶剂低。

    The lowering of the vapor pressure depends on the number of solute particles that have been dissolved. The chemical nature of the solute is not important because the vapor pressure is merely a physical property of the solvent. The only requirement is that the solute only dissolved and does not undergo a with the solvent. 
    ::蒸气压的降低取决于溶解溶解的溶液粒子的数量。溶液的化学性质并不重要,因为蒸气压力只是溶剂的物理属性。唯一的要求是溶液只溶解,溶剂不溶解。

    While the chemical nature of the solute is not a factor, it is necessary to take into account whether the solute is an electrolyte or a nonelectrolyte . Recall that are strong electrolytes and thus dissociate into when they dissolve. This results in a larger number of dissolved particles. For example, consider two different solutions of equal . One is made from the ionic compound sodium chloride, while the other is made from the molecular glucose. The following equations show what happens when these solutes dissolve.
    ::虽然溶液的化学性质不是一个因素,但有必要考虑溶液是电解剂还是非电解剂。回顾强烈的电解剂,在溶解时分离出来。这导致更多的溶解粒子。例如,考虑两种不同的溶液。一种是离子化合物氯化钠,另一种是分子溶胶。以下的公式显示溶液溶解后会发生什么情况。

    NaCl ( s ) → Na + ( a q ) + Cl − ( a q ) 2   dissolved particles C 6 H 12 O 6 ( s ) → C 6 H 12 O 6 ( a q ) 1   dissolved particle

    ::NaClNa+(aq)+Cl-(aq)2溶解粒子C6H12O6(s)C6H12O6(aq)1溶解粒子

    The sodium chloride dissociates into two ions, while the glucose does not dissociate. Therefore, equal concentrations of each solution will result in twice as many dissolved particles in the case of the sodium chloride. The vapor pressure of the sodium chloride solution will be lowered twice the amount as the glucose solution.
    ::氯化钠分解成两离子,而葡萄糖不分解。因此,每种溶液的浓度相等,氯化钠的溶解粒子数量将是氯化钠的两倍。氯化钠溶液的蒸气压力将比葡萄糖溶液的含量降低一倍。

     

     

    Summary
    ::摘要

    • Addition of a nonvolatile solute to a solution lowers the vapor pressure of the solution.
      ::在解决方案中添加非挥发性溶液会降低解决方案的蒸发压力。

    Review
    ::回顾

    1. The boiling point of diethyl ether is 34.6°C. Would this compound be considered non-volatile?
      ::二乙醚的沸点为34.6°C。 这种化合物是否可被视为非挥发性?
    2. How does the number of solute particles influence vapor pressure?
      ::溶液粒子的数量如何影响蒸气压力?
    3. Which solution will have a lower vapor pressure, a 1.0 M NaCl solution or 1.0 M CaCl 2 solution? Note: Both NaCl and CaCl 2 are non-volatile substances that dissociate in water.
      ::哪种溶液将具有较低的蒸气压力、 1.0 M NaCl溶液或1.0 M CaCl2溶液? 注意: NaCl 和 CaCl2 均为分解于水中的非挥发性物质。