• Exothermic reactions

An exothermic reaction is one in which heat is given off to the surrounding. In this case, the energy of the reactants is, greater than that of the products or the energy liberated during bond making is more than that absorbed during bond breaking. Hence the heat change is negative.

Some examples of exothermic reactions include;

• The precipitation reaction between aqueous silver nitrate and sodium chloride.

Energy level diagrams

Energy level diagrams can be used to represent exothermic and endothermic reactions.

For a reaction to occur, particles must have a minimum amount of energy to start the reaction

This minimum amount of energy that a body has to start a reaction is called energy of activation (Ea) or energy barrier.

For an exothermic system, the energy of the reactants is greater than that of the products. This can be represented on an energy level diagram as follows:.

On the graph, the energy given-off during bond making is more than that absorbed during bond breaking, thus, the overall heat change is the released of heat hence the reaction is exothermic.

For an endothermic system, the energy of the products is greater than that of the reactants. This can also be represented on an energy level diagram as below.

On the graph, the energy absorbed during bond breaking is more than that given-off during bond making, thus the overall heat change is an absorption of heat making the reaction endothermic.