Agas barbecue burns propane gas to generate heat. propane gas becomes carbon dioxide gas and water vapor as it burns. oxygen from the air is a reactant in this process. this is an example of a chemical reaction.
why is burning propane gas a chemical reaction?

the atoms that make up propane and oxygen change into different atoms after the reaction.

the water vapor that forms after the reaction is in the gas phase.

the atoms in propane and oxygen rearrange to form other substances after the reaction.

oxygen is involved. any process involving oxygen is a chemical reaction.