Chemical reactions are processes where reactants transform into products, classified mainly into five types. Synthesis reactions combine simple substances into more complex ones. Decomposition reactions break down compounds into simpler substances. Single displacement reactions involve an element replacing another in a compound. Double displacement reactions see the exchange of components between two compounds. Combustion reactions involve a substance reacting with oxygen to release energy, usually in the form of light or heat. Each type provides a unique pathway for chemical transformations, essential for understanding and controlling chemical processes in nature and industry.