Illustrated Glossary of Organic Chemistry

Gas phase: In organic chemistry, this term generally refers to a space or process which is completely gaseous. Some chemical reactions are best conducted when all of the reactants are gaseous. For example, the industrial scale free radical chlorination of methane is generally conducted in the gas phase by this reaction: CH4(g) + Cl2(g)  → CH3Cl(g) + HCl(g). Many of the processes used to produce the fuel in an oil refinery are also conducted in the gas phase.

In an internal combustion engine, fuel is vaporized before being ignited and combusted in the gas phase in each engine cylinder. Click here to see a video of how a car engine works.