Exothermic and Endothermic Reactions

Understanding Exothermic and Endothermic Reactions

Exothermic and endothermic reactions are different ways that chemical energy can change during a chemical reaction.
Exothermic reactions release energy to the surroundings, usually in the form of heat. Examples include combustion, neutralisation reactions, and many oxidation reactions.
Endothermic reactions take in energy from the surroundings. This is usually in the form of heat energy. Examples include thermal decomposition and the reaction between sodium carbonate and ethanoic acid.

Energy Changes in Reactions

In an exothermic reaction, the energy needed to break the old bonds in the reactants is less than the energy released when the new bonds of the products are formed. Hence, heat is released.
In an endothermic reaction, the energy needed to break the old bonds in the reactants is more than the energy released when new bonds are formed in the products. As a result, energy is absorbed from the surroundings.

Reaction Profiles

Reaction profiles or energy level diagrams can be used to show energy changes during a reaction.
In the graph of an exothermic reaction, the products have less energy than the reactants. The difference in energy levels is the energy released to the surroundings.
In the graph of an endothermic reaction, the products have more energy than the reactants. The difference in energy levels is the energy absorbed from the surroundings.

Everyday Examples

Exothermic reactions occur in everyday activities such as burning fuel, digestion of food, and using an instant heat pack.
Endothermic reactions occur in processes such as cooking, evaporation of water, and using a sports injury ice pack.

Measuring Energy Changes

Simple calorimetry can be used to measure the heat released or absorbed in chemical reactions.
The heat transferred to the surroundings (for exothermic) or the heat absorbed from the surroundings (for endothermic) can change the temperature of a known quantity of water. This change can then be used to calculate the energy change in the reaction.

Remember, while these energy changes may seem abstract, they’re integral to understanding how different reactions occur and the amount of energy they use or produce.