Henry's law

In chemistry, a law formulated by William Henry: the solubility of a gas in a liquid at any given temperature is proportional to the pressure of the gas on the liquid. This has wide application, including the production of carbonated beverages, and in ‘the bends’, a condition in deep-sea divers where nitrogen, having dissolved in the blood at high pressure, is released with sometimes fatal consequences when the diver returns to the low pressure of the surface.

Formula and Henry constant

A formula for Henry's Law is:

where:

p = the partial pressure of the solute above the solution c = the concentration of the solute in the solution (in one of its many units) k = the Henry's Law constant, which has units such as L·atm/mol, atm/(mol fraction) or Pa·m3/mol.

Table 1: Some forms of Henry's law and constants (gases in water at 298K), derived from

equation:
dimension:
O2	1.3 E-3	769.23	4.259 E4	3.180 E-2
H2	7.8 E-4	1282.05	7.099 E4	1.907 E-2
CO2	3.4 E-2	29.41	0.163 E4	0.8317
N2	6.1 E-4	1639.34	9.077 E4	1.492 E-2
He	3.7 E-4	2702.7	14.97 E4	9.051 E-3
Ne	4.5 E-4	2222.22	12.30 E4	1.101 E-2
Ar	1.4 E-3	714.28	3.955 E4	3.425 E-2
CO	9.5 E-4	1052.63	5.828 E4	2.324 E-2

where:

caq = moles of gas per liter of solution Lsoln = liters of solution pgas = partial pressure of gas above the solution, in atmospheres of absolute pressure xaq = mole fraction of gas in solution = moles of gas per total moles ≈ moles of gas per mole of water atm = atmospheres of absolute pressure

As can be seen by comparing the equations in the above table, the Henry's Law constant kH,pc is simply the inverse of the constant kH,cp.

The following table lists some values for constant C (dimension of kelvins) in the equation above:

Table 2: Values of C

Gas	O2	H2	CO2	N2	He	Ne	Ar	CO
C	1700	500	2400	1300	230	490	1300	1300

It can be seen, that the solubility of gases is decreasing with increasing temperature.