Energy is transferred when chemical bonds are broken or are formed.
|Breaking bonds||Forming bonds|
|Type of process||Endothermic||Exothermic|
|Heat energy transferred||Taken in||Given out|
During a chemical reaction:
The difference between the energy needed to break bonds, and the energy released when new bonds are made, determines the type of reaction.
A reaction is exothermic if more heat energy is released in making the bonds in the products, than is absorbed when breaking bonds in the reactants
A reaction is endothermic if less heat energy is released in making bonds in the products than is absorbed when breaking bonds in the reactants.