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.
The reaction ( 2 \text{H}_2(g) + \text{O}_2(g) \rightarrow 2 \text{H}_2\text{O}(g) ) represents the combustion of hydrogen gas in the presence of oxygen gas to produce water vapor. This is an exothermic reaction, meaning it releases energy, typically in the form of heat and light. It is also a redox reaction, where hydrogen is oxidized and oxygen is reduced.
CH4g + H2Og COg + 2H2g