Difference Between Endothermic and Exothermic Reactions

Such chemical reaction in which the energy is absorbed in the form of heat is known as the endothermic reaction, while such chemical reactions in which energy is released or evolved in the form of heat is known as the exothermic reaction. So the main difference between these terms lies in the form of energy used or released during any chemical reaction.

Chemical reactions not only takes place in laboratories, they happen in ones day to day routines, in our body also. For instance melting of ice cubes or evaporation of liquid water is an endothermic reaction, on the other hand, if the water freezes into ice cubes it is called as an exothermic reaction.

There is a lot of energy requirement during any chemical reactions, which exist in the bond holding the molecules together. So when the reaction takes place between molecules and compounds (reactants), which results in breaking of bonds and thus releases immense energy.

On the other hand, the new chemical bonds (products) which are formed after the reaction also requires energy and hence the total energy is calculated by the number of bonds broken and formed. This process in the chemical reaction is termed as a heat of reaction also known as enthalpy and is denoted by ‘ΔH‘. and expressed in kJ/mol.

In this content, we will be focusing on the key differences between the two terms along with few examples and with the brief description of them.

Content: Endothermic Vs Exothermic Reaction

1. Comparison Chart
2. Definition
3. Key Differences
4. Conclusion

Comparison Chart

Basis for Comparison	Endothermic Reactions	Exothermic Reactions
Meaning	Chemical reactions involving the use of energy at the time of dissociation to form a new chemical bond is known as the endothermic reaction.	Chemical reactions where the energy is released or evolved in the form of heat is known as the exothermic reaction.
Energy	The endothermic process requires energy in the form of heat.	The exothermic process evolves or releases in the form of heat.
Enthalpy (ΔH)	ΔH is positive, as heat is absorbed.	ΔH is negative, as heat is evolved.
Examples	1. Conversion of ice into water vapour through boiling, melting or evaporation. 2. Breaking of the gas molecules. 3. Production of anhydrous salt from hydrate.	1. Formation of ice from water. 2. Burning of coal (combustion). 3. The reaction between water and the strong acid.

Definition of Endothermic Reaction

As the name suggests, ‘endo‘ means ‘to absorb’ while ‘thermic‘ refers to ‘heat’. So we can define the endothermic reactions as such chemical reaction where the energy is absorbed during the conversion of reactant into the product. This happens because of the dissociation of the bonds between the molecules. Later on, the energy is released, when the new bonds are formed.

In the endothermic reaction, the products contain more energy than the reactants. In these reactions, the heat is taken up from the surroundings, due to which the temperature of the system where the reaction is going remains cooler. Even the enthalpy (ΔH) which is defined as the change in heat energy during the conversion of reactants to the products becomes higher at the end of the reaction.

The value of ΔH or DH or DE is always positive.

Few common examples of endothermic reactions are:
1. Photosynthesis – The process where chlorophyll present in green plants in converted the water and carbon dioxide into the glucose and oxygen, in the presence of sunlight, which works as the energy provider.

2. When the small amount of ammonium chloride (NH4Cl) is taken in a test tube and is made to dissolve in water, we observed that the test tube becomes colder. In this reaction, the heat is absorbed from its surrounding (test tube).

3. Conversion of ice into water through boiling, melting or evaporation

Definition of Exothermic Reaction

Here ‘exo‘ refers ‘to release or to evolve’, and ‘thermic‘ refers to ‘heat’. Hence exothermic reaction can be defined as such chemical reaction where the energy is released or evolved. These types of reactions are warmer, and sometimes they are dangerous feel if the reaction is at the higher rate.

In an exothermic reaction, the amount of energy released during the formation of new bonds (product) is higher than the total amount of energy needed while breaking up the bonds (reactants). This is the reason for heating of the system or reactions. Even the enthalpy change becomes lower at the end of the reaction.

The value of ΔH or DH or DE is always negative.

Few common examples of endothermic reactions are:
1. Combustion – Burning of coal, a candle, sugar.
2. When laundry detergent is dissolved in water, or when water is added to the quicklime while preparing whitewash. In such reaction, there is the production of the ample of heat, which warms up the water.
3. Formation of ice from water.
4. Respiration, digestion of food.

Conclusion

From the above article, we conclude that there are various types of reactions which takes place, whenever molecules interact with each other. Endothermic and Exothermic reactions are the two types of chemical reactions categorized by their behaviour during the chemical reaction, and we found these words opposite of each other.