Henry's law

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In chemistry, Henry's law is one of the gas laws. 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.

A formula for Henry's Law is:

where:

P = the partial pressure of the gaseous solute above the solution
C = the concentration of the dissolved gas in mol/L
k = the Henry's Law constant, which has units such as J/mol,L·atm/mol or Pa·m^3/mol.

Taking the natural logarithm of the formula, gives us the more commonly used formula:

This version is used to showcase the effectiveness of the law for dilute solutions of gases that don't react with the solvent. Some values for k include:

O₂ : 4.34×10⁴ L·atm/mol
CO₂ : 1.64×10³ L·atm/mol
H₂ : 7.04×10⁴ L·atm/mol

when these gases are dissolved in water at 299 kelvins. Note that the solubility coefficient varies with solvent and temperature.

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Henry's law in geophysics

A version of Henry's law applies to the solubility of a noble gas in contact with silicate melt. One equation used is

<math>

\rho_m/\rho_g=e^{-\beta(\mu_{{\rm ex},m}-\mu_{{\rm ex},g})}</math>

where:

subscripts m = melt
subscript g = gas phase
<math>\rho</math> = the number densities of the solute gas in the melt and gas phase
<math>\beta=1/k_BT</math> an inverse temperature scale
- <math>k_B</math> = the Boltzmann constant
<math>\mu_{{\rm ex},m}</math> and <math>\mu_{{\rm ex},g}</math> = the excess chemical potential of the solute in the two phases.

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