A gas evolution reaction is a chemical reaction that results in the production of a gas. For example, a gas evolution reaction potentially produces oxygen or carbon dioxide.
It is sometimes possible to tell that a chemical reaction has occurred by observation of the newly formed products and their new chemical properties. The evolution of a gas is one of several possible results of a chemical reaction. According to Rhode Island College, others include the emission of heat or light, a change in color or the formation of a precipitate. A chemical reaction that produces at least one gas as a product is considered a gas evolution reaction.