Explain the equilibrium of gases in liquids.

(N/A) The equilibrium of gases in liquids is best illustrated by a closed soda water bottle containing $CO_{2}$ gas under high pressure. An equilibrium exists between the $CO_{2}$ molecules dissolved in the liquid and those in the gaseous state:
$CO_{2(g)} \rightleftharpoons CO_{2(aq)}$
This process is governed by Henry's Law,which states that at a constant temperature,the mass of a gas dissolved in a given volume of solvent is directly proportional to the partial pressure of the gas above the solvent surface:
$\text{Solubility} \propto \text{Pressure} \text{ (at constant } T\text{)}$
When the bottle is sealed,the high pressure of $CO_{2}$ ensures high solubility. Upon opening the bottle,the pressure above the liquid drops to atmospheric pressure. Consequently,the equilibrium shifts to the left,causing dissolved $CO_{2}$ to escape as gas until a new equilibrium is established at the lower partial pressure. This loss of dissolved gas is why soda water becomes 'flat' when left open.