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Difference Between Endothermic and Exothermic Reactions

Endothermic vs Exothermic Reactions

Energy is the capacity to do work. In a system, energy can do work, and in this process, energy can be changed to other forms such as heat, sound, light etc. When the energy of a system changes as a result of a temperature difference between the system and the surrounding we say that energy has been transferred as heat. A chemical reaction can be considered as a system. Chemical reaction is a process, where one or more compounds are converted to a new set of compounds through a series of changes. When the reaction proceeds, there can be a heat transfer from surrounding to the system or vice versa. Endothermic reaction is a process in which energy is acquired from its surrounding to the system, while exothermic reaction is a process that releases energy from the system to the surrounding.

Exothermic Reaction

Exothermic reaction is a process that releases energy to the surroundings, usually in the form of heat. The energy can also be released in other forms such as sound, light etc. Because the energy is released during the reaction, the products contain less energy than the reactants. Therefore, the enthalpy change (∆H) becomes negative. Energy is released during bond formation. If the total bond formation energy is higher than bond breaking energy during the reaction, then it is exothermic. If the energy is released as heat, the surrounding temperature goes up, so sometimes the reaction can be explosive. Exothermic reactions are spontaneous. Thus, an outside energy supply is not necessary for exothermic reactions, because they produce the required energy as the reaction proceeds. However, to start the reaction, an initial energy supply may be necessary. If this released energy can be captured, lot of useful work can be done. For an example, the energy released from the combustion of fuels can be taken to operate a vehicle or a machine. Moreover, all combustion reactions are exothermic.

Endothermic Reaction

Endothermic reaction is a process in which energy is acquired from its surroundings, in the form of heat. If the surrounding doesn’t supply heat, the reaction may not proceed. The reaction vessel gets cold, because heat is absorbed from the surrounding environment, thereby lowering the temperature. Energy is required for bond breaking. In endothermic reactions, the bond breaking energy of reactants is higher than the total bond formation energy of the products. Therefore, enthalpy change is a positive value, and the reaction is not spontaneous. So, for endothermic reactions, we have to supply energy from outside. For example, when dissolving ammonium chloride in water, the beaker gets cold, because the solution absorbs energy from the outside environment. Photosynthesis is an endothermic reaction which takes places in the natural environment. For photosynthesis energy is supplied by sunlight.

Exothermic Reactions Vs Endothermic Reactions

- Endothermic reactions absorb energy from the surrounding environment, whereas in exothermic reactions energy is released to the surroundings.

- The enthalpy change for exothermic reactions is negative, and for the endothermic reactions it is positive.

- Usually, the spontaneous direction of a reaction is exothermic, and the reverse of the same reaction is endothermic.

- In endothermic reactions, the products have a higher energy compared to the energy of the reactions. Therefore, products are less stable than the reactants. In exothermic reaction, the products are more stable than the reactants, because their energy is lower than reactants’ energy.


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