Endothermic and Exothermic Reactions

When chemical reactions occur, they are accompanied by a transfer of energy, sometimes to and sometimes from the surroundings, which can often take place in the form of a temperature change. An endothermic reaction is one that results in the absorption of heat and an exothermic one is the exact opposite, a chemical reaction that releases heat. Essentially, in an exothermic reaction, there is surplus energy which is released in the form of heat once the reaction is complete. Exothermic reactions may occur spontaneously and can also be used under controlled situations to produce explosions. Endothermic reactions, on the other hand, are those in which the energy required for the reaction to take place is insufficient. In this case, the heat is absorbed to make up for this deficit (these reactions should not be confused with endergonic reactions in which the energy absorbed need not be in the form of heat). So now that you know a little about endothermic vs exothermic reactions, to illustrate the difference between them more clearly, following are some examples.

Examples of Endothermic Reaction

Many endothermic and exothermic reactions are those we encounter regularly. Once you understand the principle behind endothermic reactions, chemical reactions in everyday life will show you many examples of reactions which need heat. In an endothermic reaction, the resultant product has higher energy than the reactants. To make up for the energy deficit, the product absorbs heat from the surroundings, resulting in a drop in temperature. These reactions are generally not spontaneous. Following are some illustrations to get you started:

Photosynthesis
Photosynthesis is one of the best illustrations of endothermic reactions occurring in nature. It is a process in which plants use chlorophyll in the presence of sunlight to convert carbon dioxide and water to glucose and oxygen.

Melting Ice
When ice melts, it draws heat from the surroundings rendering the solid form unstable.

Water Evaporation
Another natural example of an endothermic reaction. Water in the liquid form uses heat to convert into the gaseous form of vapor.

Electrolysis
Electrolysis involves the separation or decomposition of the original compounds which occurs as a result of the application of an electric current.

Examples of Exothermic Reaction

Exothermic reactions are types of chemical reactions which result in the release of energy on completion. In simple terms, the reactants contain more energy than the product. This surplus energy is released in the form of heat. These reactions are often spontaneous, however in chemical terms, 'spontaneous' is not synonymous with 'fast'. Spontaneous is indicative of denoting that an exothermic reaction can take place without the external application of energy, as against the case of endothermic reactions. Following are some examples of exothermic reactions:

Combustion/Burning
When you light a match or a fire, the compounds that burn, release heat into the surroundings causing an increase in temperature. This is the most basic illustration of an exothermic reaction. Combustion of fuel is another such example.

Neutralization
Many (but not all) neutralization reactions are exothermic in nature. A neutralization reaction is one that takes place between an acid and a base to produce salt and water. For example, mixing sodium hydroxide (a base) with hydrochloric acid (the acid) will give you a solution of sodium chloride and water, accompanied by an increase in temperature.

Rusting
Rusting of iron is also an example of a spontaneous exothermic reaction.

Endothermic and exothermic reactions are basic concepts of thermochemistry, many examples of which can be seen in daily life. I hope this article helped you understand the difference between them clearly.