An exergonic reaction is a type of reaction where energy is released to the surroundings. This reaction happens spontaneously and does not require energy to proceed. These reactions form more stable bonds by breaking less stable chemical bonds and release energy. Catabolic reactions are exergonic reactions. Here energy is released by the breaking down of larger molecules into smaller ones. Cellular respiration is an example of an exergonic (catabolic) reaction. It is the conversion of glucose in the presence of oxygen into carbon dioxide and water. The energy released is used for cell activities. Another example is the breaking down of hydrogen peroxide into water and oxygen in the cells.
An endergonic reaction is a type of reaction where energy is absorbed from the surroundings. These reactions form less stable bonds by breaking more stable chemical bonds using energy. Anabolic reactions are endergonic, in which small molecules combine to form larger ones. An example of an anabolic reaction is photosynthesis, where carbon dioxide and water are used to produce glucose and oxygen by using energy from sunlight. Another example is the reaction of glycerol with fatty acids to make lipids.
