Endothermic reaction

In Chemistry an endothermic reaction is one in which the products have less energy than the reactants, and thus a net input of energy, usually in the form of heat, is required. Endothermic reactions are often described as reactions that "feel cold", and contrast with exothermic reactions, in which heat is released. Although the process of bond breaking amongst reactants in a chemical process requires an initial input of energy (the activation energy), in the case of an endothermic reaction, the energy released when bonds are formed to create reactants is less than that required to break the bonds in the products; bonding electrons in the products are therefore at a higher energy than the reactants. Heat energy from the material surrounding the reactants is usually what breaks their bonds, so as heat energy is transferred from the surroundings to the reactants, the surroundings get colder. This is often summarized in a chemical equation as follows:

Reactants + Energy → Products

Examples of endothermic reactions

Reactions within food when cooking.

Respiration reaction

The polymerization of ethene to polythene.

The reduction of silver ions to silver.

Electrolysis. Energy is provided in the form of electricity.

The mixing of barium hydroxide and ammonium thiocynate causes a powerful endothermic reaction that causes the products to become so cold that the moisture from the air forms a layer of frost on the outer surface of the beaker.

Reactions in an aqueous solution. Heat energy is transferred from the water to the reactants. In this way, the temperature of the solution falls.

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Examples of endothermic reactions

See also