The equation (2 \text{H}_2\text{g} + \text{O}_2\text{g} \rightarrow 2 \text{H}2\text{O}{\text{i}}) describes the chemical reaction of hydrogen gas ((H_2)) reacting with oxygen gas ((O_2)) to form liquid water ((H_2O)). This is a combustion reaction where two molecules of hydrogen gas combine with one molecule of oxygen gas to produce two molecules of water. The reaction is exothermic, releasing energy in the form of heat.