A chemical reaction is a process involving the rearrangement of the molecular structure of a substance, resulting in the formation of one or more new substances with different chemical compositions from the initial reactants. These transformations occur through the breaking of existing chemical bonds and the formation of new ones between atoms. The feasibility and rate of a reaction are governed by factors such as temperature, pressure, and the concentration of substances, often requiring an initial input of energy known as activation energy. The overall reaction determines the change in enthalpy and entropy, defining whether the process is exothermic, endothermic, or involves electrochemical changes. Chemical reactions are fundamental to all natural processes, including metabolic pathways, and are the basis for numerous industrial and technological applications.