亨利定理和道尔顿定理

亨利定理和道尔顿定理

2007年05月29日星期二 15:01

亨利定律Henry's law

在一定温度下，气体在液体中的饱和浓度与液面上该气体的平衡分压成正比。它是英国的W.亨利于1803年在实验基础上发现的经验规律。实验表明，只有当气体在液体中的溶解度不很高时该定律才是正确的，此时的气体实际上是稀溶液中的挥发性溶质，气体压力则是溶质的蒸气压。所以亨利定律还可表述为：在一定温度下，稀薄溶液中溶质的蒸气分压与溶液浓度成正比：

pB＝kxB

式中pB是稀薄溶液中溶质的蒸气分压；xB是溶质的物质的量分数； k为亨利常数，其值与温度、压力以及溶质和溶剂的本性有关。由于在稀薄溶液中各种浓度成正比，所以上式中的xB还可以是mB（质量摩尔浓度）或cB（物质的量浓度）等，此时的k值将随之变化。

只有溶质在气相中和液相中的分子状态相同时，亨利定律才能适用。若溶质分子在溶液中有离解、缔合等，则上式中的

xB（或mB、cB等）应是指与气相中分子状态相同的那一部分的含量；在总压力不大时，若多种气体同时溶于同一个液体中，亨利定律可分别适用于其中的任一种气体；一般来说，溶液越稀,亨利定律愈准确，在xB→0时溶质能严格服从定律。

道尔顿气体分压定律

在任何容器内的气体混合物中，如果各组分之间不发生化学反应，则每一种气体都均匀地分布在整个容器内，它所产生的压强和它单独占有整个容器时所产生的压强相同。也就是说，一定量的气体在一定容积的容器中的压强仅与温度有关。例如，零摄氏度时，1mol 氧气在 22.4L 体积内的压强是 101.3kPa 。如果向容器内加入 1mol 氮气并保持容器体积不变，则氧气的压强还是 101.3kPa，但容器内的总压强增大一倍。可见， 1mol 氮气在这种状态下产生的压强也是101.3kPa 。

道尔顿（Dalton）总结了这些实验事实，得出下列结论：某一气体在气体混合物中产生的分压等于它单独占有整个容

器时所产生的压力；而气体混合物的总压强等于其中各气体分压之和，这就是气体分压定律（law of partial pressure）。Henry's law

In chemistry, Henry's law is one of the gas laws, formulated by William Henry. It states that: At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

Dalton's law

In chemistry and physics, Dalton's law (also called Dalton's law of partial pressures) states that the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in a gas mixture. This empirical law was observed by John Dalton in 1801 and is related to the ideal gas laws.

Mathematically, the pressure of a mixture of gases can be defined as the summation

P total =P1+P2+…+Pn

Where P1, P2, Pn represent the partial pressure of each component.

It is assumed that the gases do not react with each other.

Pi=P total Xi

Where Xi = the mole fraction of the i-th component in the total mixture of m components.

The relationship below provides a way to determine the volume based concentration of any individual gaseous component.

Pi=P total Ci/1000000

Where, Ci is the concentration of the i-th component expressed in ppm.

Dalton's law is not exactly followed by real gases. Those deviations are considerably large at high pressures. In such conditions, the volume occupied by the molecules can become significant compared to the free space between them. Moreover, the short average distance between molecules raises the intensity of intermolecular forces between gas molecules enough to substantially change the pressure exerted by them. Neither of those effects are considered by the ideal gas model.

Henry's law

In chemistry, Henry's law is one of the gas laws, formulated by William Henry. It states that:

At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

Formula and Henry constant

A formula for Henry's Law is: