Difference Between Endothermic and Exothermic Reaction

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Endothermic and Exothermic Reaction (Differences)

An endothermic reaction requires energy while an exothermic reaction releases energy. This classification of chemical reactions takes into account the participation of energy either as a reactant or as a product.

Energy is the ability to do work or to produce heat. Remember that chemical reactions involve a reorganization of atoms between substances with breakage or formation of chemical bonds.

In general, this formation or breaking of chemical bonds is accompanied by changes in the energy of the system.

What are the Differences Between Endothermic and Exothermic Reaction?

Endothermic Reaction Exothermic Reaction
Definition Chemical reaction where energy is absorbed. Chemical reaction where energy is released in the form of heat.
Origin of energy Of the environment Of the system
Potential energy Lower in reactants than in products. Higher in reactants than in products.
Production Not spontaneous Spontaneous
Internal energy change ΔE> 0; internal energy change greater than zero. ΔE <0; internal energy change less than zero.
Temperature Decreases Increases
Examples Reactions in photosynthesis and synthesis in general. A burning match, combustion reactions.
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What is an Endothermic Reaction?

A chemical reaction is endothermic when it absorbs energy from the environment. In this case, the heat is transferred from the outside to the inside of the system. When we place a thermometer while the endothermic reaction is taking place, the temperature drops.

The word “endothermic” derives from the Greek endon which means “inside” and therme which means “heat“. Endothermic reactions do not proceed spontaneously.

Where does the energy come from in Endothermic Reactions?

Difference Between Endothermic and Exothermic Reaction
Energy diagram of a general endothermic reaction.

In endothermic reactions, the energy comes from the environment outside the system. The amount of potential energy of the products is greater than the potential energy of the reactants. Therefore, it is required to add energy to the reactants for the reaction to proceed. This energy comes from the heat of the environment.

For example, photosynthesis is an endothermic process, where plants capture solar energy to produce glucose from carbon dioxide and oxygen:

endothermic reaction

The products of the photosynthesis reaction, glucose and oxygen, have a greater amount of potential energy with respect to the reactants, carbon dioxide and water. Other examples of endothermic chemical reactions with the amount of energy used:

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examples of endothermic reaction

Examples of Endothermic Reaction

It is not only in the chemistry laboratory that reactions occur. On a day-to-day basis, we also find situations where endothermic reactions occur.

Cooking Food – Endothermic Reaction

Although it may not seem like it, the process of cooking food is endothermic. In order to consume certain foods, we must provide heat.

Instant Cold Bag – Endothermic Reaction

Cold packs used to treat bumps or sprains are filled with water, but when shaken or knocked, a capsule containing ammonium nitrate breaks inside. Mixing ammonium nitrate with water is an endothermic reaction, causing the bag to cool.

What is an Exothermic Reaction?

An exothermic reaction is one where energy flows out of the system. This energy is released in the form of heat, so placing a thermometer in the reaction system increases the temperature.

The word “exothermic” is formed by exo which means “outward” and thermes, which means “heat“. Exothermic reactions can occur spontaneously and, in some cases, be explosive, such as the combination of alkali metals and water.

Where does the energy come from in Exothermic Reactions?

exothermic reaction potential energy difference
In a chemical reaction, reactants are the compounds that transform and give rise to products. For example, when sodium Na reacts with chlorine Cl, these are the reactants and the product is sodium chloride NaCl:

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exothermic reaction

Both reactants and products have stored potential energy. We know from the energy conservation law that energy is neither lost nor gained, so the energy of the reactants must be equal to that of the products.

In an exothermic reaction, reactants have more potential energy compared to products, so excess energy is released as heat. In this case, energy is also considered as part of the products:

exothermic reaction

In any exothermic process, part of the potential energy stored in chemical bonds is converted into thermal energy through heat.

Examples of Exothermic Reaction

  • Laundry Detergent

When we dissolve a little washing powder with water in our hands we can feel a slight heating.

  • Domestic Gas Combustion

The combustion of gases for domestic use, such as methane or butane, involves the chemical reaction with oxygen with the formation of carbon dioxide and water, and the release of energy. This is a typical exothermic reaction in everyday use:

butane combustion chemical equation exothermic reaction

The energy released in the combustion process is used to cook food.


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