Gas-Dissolved Gas in Equilibrium
Gases are soluble in liquids. For a given pair of gas and liquid, solubility depends on temperature and pressure. For a given temperature and pressure, the solubility of a gas increases with the ease of liquefaction of the gas. For example, hydrogen and helium are much less soluble in water than carbon dioxide and ammonia. Dissolution of a gas in a liquid is generally an exothermic process. Consequently, the solubility of a gas decreases with increase in temperature. The effect of gaseous pressure on its solubility as given by Henry's law is
m p or m = kp
that is, at a given temperature, the mass of dissolved gas in a given volume of solvent is proportional to the pressure of the gas with which it is in equilibrium. There exists equilibrium between the gas in gaseous phase and the gas that has dissolved in the liquid phase, i.e.
Gas (gaseous phase) Gas (in liquid phase)