化学专业英语马永祥翻译36课

36 沸点和蒸馏Boiling Points of Pure Liquids沸点的纯液体Any given liquid, when admitted into a closed evacuated space, evaporates until the vapor attains a certain definite pressure, which depends only upon the temperature. This pressure, which is the p ressure exerted by the vapor in equilibrium with the liquid, is the vapor pressure of the liquid at th at temperature. As the temperature increases . the vapor pressure of a typical liquid x increases reg ularly as shown by the generalized vapor pressure-temperature curve BC, in Fig. 5.任何给定的液体,当进入一个封闭的疏散空间,蒸发到蒸汽形成某种明确的压力,仅仅依赖于温度。

这种压力,这是由蒸汽压力与液体平衡的,是液体的蒸气压在温度。

随着温度的升高。

这个压力，是通过在与液体平衡的蒸汽施加的压力，是液体在该温度下的蒸汽压，其随着温度的增加而增加。

一个典型液体x的蒸汽压的增加经常如图五所示，广义蒸汽压-温度曲线BC。

At the temperature, Tp, where the vapor pressure reaches 101.3kPa. x begins to boil and Tp is call ed the NORMAL BOILING POINT of x. Every liquid which does not decompose before its vapor pressure reaches 101.3kPa. has its own characteristic boiling point. In general, the boiling point of a substance depends upon the mass of its molecules and the strength of the attractiveforces between them. For a given homologous series, the boiling points of the member compounds rise fairly regularly with increasing molecular weight.在温度、Tp,那里的蒸汽压力达到101.3 kPa。

开始煮和x Tp被称为正常沸点液体的x。

在这个温度，当蒸汽压达到101.3 kPa时，液体x开始沸腾，这个蒸汽压力被叫做x的正常沸点。

任何一种液体在它的蒸汽压达到101.3 kPa之前都不分解，每种液体的沸点都有其自身的特点。

一般来说,一种物质的沸点取决于它的分子质量和它们之间的引力的强度。

对于一个给定的同系物，其成员化合物的沸点随分子量的增加而增加。

Polar liquids tend to boil higher than nonpolar liquids of the same molecular weight, and associated polar liquids usually boil considerably higher than nonassociated polar compounds.极性液体的沸点往往高于相同分子量的非极性液体，而相关的极性液体的沸点远远高于一般的极性化合物。

The boiling point is a characteristic constant that is widely used in the identification of liquids. Be cause of its marked dependence upon pressure and its rather erratic response to impurities, howeve r, it is generally less reliable and useful in characterization and as a criterion of purity than is the m elting point for solids1.沸点是一个常数,广泛用于识别液体。

然而，由于对压力的显著依赖性和对杂质的相当无规律的反应，沸点用于鉴别和作为纯度的判据方面，较之固体的熔点一般不太可信和较少使用。

Boiling Points of Solutions沸点的解决方案The normal boiling point of any solution is the temperature at which the total vapor pressure of the solution is equal to 101.3kPa. The effect of any solute, Y, on the boiling point of X will depend, th en, upon the nature of Y. If Y is less volatile than X. then the total vapor pressure of the solution is lower, at any given temperature, than the vapor pressure of pure X.正常沸点的任何解决方案都是在其溶液总蒸汽压力等于101.3 kPa时的温度。

任何溶质，Y 在X上的沸点的效果将取决于Y的性质。

如果Y比X难挥发。

那么其总蒸汽压都比在任何给定的温度下纯X的蒸汽压低。

Such a case is represented by curve B'C , in which the experimentally determined values tor the va por pressures of a solution are plotted against temperature. The vapor pressure of the solution does not reach 101.3kPa. until a temperature Tp' is attained. In other words, the presence of the less vol atile solute raises the boiling point of X from Tp to Tp'. A solution of sugar or salt in water is a fa miliar example of this type of solution.根据溶质所确定实验值来绘制温度-蒸汽压力图，如曲线B'C所示。

直到温度达到Tp'时，其溶液的蒸汽压才达到101.3 kPa。

换句话说,较低挥发性溶质的存在使X的沸点从Tp提高到Tp’。

这种类型的一个广为人知的例子就是糖或盐溶解在水中。

Figure 5. Generalized vapor pressure diagrams for a pure liquid (BO , for a solution in which the s olute is less volatile than the solvent (B'C), and for a solution in which the solute is more volatile t han the solvent(B"C").图5。

广义水汽压图表示纯液体(BC,溶液中溶质比溶剂(B 'C)难挥发，以及另一溶液中含有更不稳定的溶剂(B“C”)。

On the other hand, if Y is more volatile than X. then the total vapor pressure of the solution is higher than that of pure X, as shown by curve B"C". The vapor pressure of such a solution reaches 101.3kPa. at temprature Tp"; hence the effect of the more volatile solute is to lower the boiling po int of X from Tp to Tp". A solution of acetone in water is an example of this type.另一方面,如果Y比X更易挥发。

那么其溶液的总蒸汽压比纯X的高。

,如图所示曲线B’’C’’所示。

当一溶液的蒸汽压力达到101.3 kPa、温度达到Tp ",因此更多的挥发性溶质的作用是使X 的沸点从TP降低到TP’’。

丙酮在水中的溶液就是这种类型的一个例子。

In any solution of two liquids X and Y, the molecules of X are diluted by molecules of Y, and, con versely, the molecules of Y are diluted by molecules of X. You would therefore expect the vapor pressure due to X to be less than that of pure X; in fact, you might predict that the PARTIAL PRESSURE due to X would be proportional to the molecular concentration of X.在任何溶液中的两种液体X和Y，X的分子被Y的分子稀释，相反,Y的分子被X的分子稀释。