Henry's law

The Henry's law ( after the English chemist William Henry) describes the solubility of ( volatile ) substances in a liquid.

Definition

The Henry 's law states that the partial pressure of a gas above a liquid is directly proportional to the concentration of the gas in the liquid. The proportionality is expressed by the Henry's Law constant. The notation most commonly used is:

With

  • : Partial pressure of the substance
  • : Concentration in the solution (index l for liquid engl. ).

The law is compatible with the principle of Le Chatelier, as an outer pressure increase in the system will respond with a reduction in the number of particles of the gas ( reduce the pressure and therefore the "forced " to dodge ).

Different Versions

With the mole fraction x.

The different Henry's Law constants can convert into each other, for example, results

Or

Where R is the molar gas constant, and T is the temperature of the system.

Limits of validity

Strictly speaking, the Henry law bar is applicable only for small and moderate pressures up to about 5. And it is only valid for dilute solutions, ie at low partial pressures. In addition, the dissolved particles can not react with the solvent, such as carbon dioxide with water, otherwise the balance is disturbed.

Application in diving

With the relatively simple Henry's law can explain the decompression sickness in divers. The ambient pressure decreases by about 1 bar to 10 per meter of water. With increasing partial pressure more nitrogen is first dissolved in the blood that transports him into the periphery. He diffuses preferably in compartments with high fat content. Takes place too fast and the appearance without any necessary decompression, the back-diffusion of nitrogen ( = fabric > Blood => lung) is too slow, so that it disintegrates. When this occurs in the tissue, it is called " bends" (joint pain), in the pulmonary circulation of " chokes " ( breathing problems ) or bubble formation in the arteries supplying the brain or spinal cord, of " staggers " ( neurological symptoms).

William Henry (chemist) Le Chatelier's principle Bar (unit)
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