endothermic reaction

Chemical reaction that requires an input of energy in the form of heat for it to proceed; the energy is absorbed from the surroundings by the reactants. A sign that this is happening is if the container holding the reactants feels cold and the temperature of the reactants falls. The energy absorbed is represented by the symbol +ΔH.

The dissolving of sodium chloride in water and the process of photosynthesis are both endothermic changes. In photosynthesis the energy absorbed is in the form of light energy. In an endothermic reaction the energy needed to break the chemical bonds in the reactants is greater than the energy released when bonds are formed in the products. See energy of reaction.