|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 form, determines the type of reaction. A reaction is:
An energy level diagram shows these differences more clearly.
An energy level diagram shows the energy in the reactants and products, and the difference in energy between them.
The energy level decreases in an exothermic reaction. This is because energy is given out to the surroundings.
The energy level increases in an endothermic reaction. This is because energy is taken in from the surroundings.