没门化学专业英语马永祥翻译36课

2021年1月19日发(作者：传教士式)

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< br>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 attractive
forces 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< br>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，< br>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
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
101.3kPa. at temprature Tp
int of X from Tp to Tp
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. Y
ou 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。你因此会认为由此
X的蒸汽压就小于纯的
X
。事实上
,
你可以预测
,X
的局 部压力
,
与
X
的组分的浓度成正比。

Similarly, the partial pressure of Y
might be expected to be proportional to the molecular concentr
ation of Y
. This is, in fact, the relationship which holds for so -called ideal solutions. It is expresse
d in Raoult's Law-the partial pressure of a component in a solution at a given temperature is equal
to the vapor pressure of the pure substance multiplied by its mole fraction in solution. In symbols,
for a solution of components X and Y
.
同样地
,
局部压力的
Y
也许被希望是与
Y
的分子浓度成正比。
.
这是
,
事实上
,
这种关系可以使
用与理想溶液。
这 由拉乌尔定律表述为：
溶液中成分的局部压力等于在给定温度下的纯物质
的蒸汽压乘以该物质在 溶液中的摩尔分数。用符号
X
和
Y
表示溶液的组分。

Px=Px0Nx
where Px = the partial pressure of X in solution,
Px=X
在溶液中的分压

Px0= the vapor pressure of pure X at that temperature,
Px0 =
纯
X
在该温度下的蒸汽压

Nx = the mole fraction of X in the solution.
Nx =X
在溶液中的摩尔分数

Similarly.
相同的，


Py = Py0Ny
where Py = the partial pressure of Y
in solution.
Py=Y
在溶液中的分压

Py0 = the vapor pressure of pure Y
at that temperature,
Py0 =
纯
Y
在该温度下的蒸汽压

Ny = the mole fraction of y in solution.
Ny=Y
在溶液中的摩尔分数

The total pressure, PT of the solution would be the sum of the partial pressures of X and Y
.
溶液的总压 ，
PT
，是
X
和
Y
的分压的加和。

PT = Px+Py
Temperature-Composition Diagram for Solutions which Follow Raoult's
Law.

溶液的温度—组成图遵循拉乌尔定律

These facts are represented graphically in Fig. 6 which shows a typical te
mperature-composition diagram. This diagram is a temperature- compositi
on plot of the experimentally determined values for the system benzene-t
oluene, but it is representative of the plot for all solutions which are descr
ibed by Raoult's Law.
根据事实，用图
6
来表示，图
6
是一个典型的温度
-
组成图。这个图
是用实验方法对苯
-
甲 苯系统测定值而得到，但对所有可以用拉乌尔
定律来表示的溶液，这是一个典型的图。

Boiling points (ordinates) are plotted against composition expressed as m
ole fractions (abscissae). Pure benzene (100 percent x ) boils at 80.1
°
(p
oint A) and pure toluene (100 percent y ) at 110.6
°
(point B). All mixtur
es of the two boil at intermediate temperatures, as shown by the liquid (lo
wer) curve. This curve shows the temperature at which a mixture of benz
ene and toluene of any given composition begins to boil. The vapor (uppe
r) curve represents the composition of the vapor in equilibrium with the li