All chemical reactions do not require an initial input of energy called catalysis. Some reactions occur spontaneously without the need for an additional energy input. These are known as exothermic reactions and release energy in the form of heat or light. On the other hand, endothermic reactions require an input of energy to initiate the reaction, but this energy is not referred to as catalysis. Catalysis is a process in which a substance called a catalyst speeds up the rate of a chemical reaction without being consumed in the reaction.