Gas-phase reactions occur when reactants are in the gaseous state, allowing them to collide and interact freely. These reactions can involve simple molecules or complex mixtures and are often characterized by changes in temperature, pressure, and volume. The rate of a gas-phase reaction can be influenced by factors such as concentration, temperature, and the presence of catalysts. In these reactions, the products formed are also typically gases. Common examples include combustion reactions, where hydrocarbons react with oxygen to produce carbon dioxide and water vapor. Understanding gas-phase reactions is essential in fields like chemistry, environmental science, and engineering.