The general chemical equation for the complete combustion (or burning) of some hydrocarbon fuel is, in words, as follows:
hydrocarbon fuel and oxygen gas react to produce carbon dioxide gas and water vapor,
or, using chemical notation,
[tex]\mathrm{C_xH_y} + z\mathrm{O_2} \rightarrow \mathit{x}\mathrm{CO_2} + \frac{\mathit{y}}{2}\mathrm{H_2O}[/tex]
where
[tex]z = x + \frac{y}{4}.[/tex]
Don't worry if that looks daunting. In our case, we are given the identity of the fuel (methane, or CH₄), so our equations will be straightforward.
In words: Methane gas and oxygen gas react to produce carbon dioxide gas and water vapor (or methane gas + oxygen gas → carbon dioxide gas and water vapor).
In chemical notation:
[tex]\mathrm{CH_4}_{\text{(g)}} + 2\mathrm{O_2}_{\text{(g)}} \rightarrow \mathrm{CO_2}_{\text{(g)}} + 2\mathrm{H_2O}_{\text{(g)}}.[/tex]
