The phenomenon that occurs when two different substances are mixed and produce a result is known as a chemical reaction. In this process, the original substances, called reactants, undergo a transformation to form new substances, termed products. Chemical reactions can involve changes in energy, color, temperature, or state. Examples include combustion, oxidation, and acid-base reactions. Understanding these reactions is fundamental in fields such as chemistry, biology, and materials science, as they illuminate how substances interact and how new materials can be created.