Move the slider along to see the breaking and forming of bonds and the energy changes including activation energy along the reaction path.   Click the button to change the reaction example.When molecules react with one another the reaction can be thought of as taking place in two stages. First the breaking of bonds in the reactants. Secondly the making of new bonds in the product.

In the reaction between hydrogen and chlorine to make hydrogen chloride  more energy is released than was put in to break bonds. The net energy change is a release to the surroundings. We call this an exothermic reaction.

The reaction between nitrogen and oxygen to form nitric oxide is an example of a reaction where more energy is used in breaking bonds than is released by the formation of new bonds. There is a net transfer of energy from the surroundings to the reaction system. This is called an endothermic reaction.

Test your knowledge of energy diagrams.

Calculate values for these reactions