The key difference between endothermic and exothermic reactions is that endothermic reactions absorb energy from the surrounding environment, whereas exothermic reactions release energy to the surrounding environment.
Energy is the capacity to do work. In a system, energy can do work; it can change into 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. An endothermic reaction is a process in which energy is acquired from its surrounding to the system, while an exothermic reaction is a process that releases energy from the system to the surrounding.
CONTENTS
1. Overview and Key Difference
2. What are Endothermic Reactions
3. What are Exothermic Reactions
4. Side by Side Comparison – Endothermic vs Exothermic Reactions in Tabular Form
5. Summary
What are Endothermic Reactions?
An 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 does not occur. During this reaction, the reaction vessel gets cold because it absorbs heat from the surrounding environment, thereby lowering the temperature.
To break a chemical bond, it needs energy. In endothermic reactions, the bond-breaking energy of reactants is higher than the total bond formation energy of the products. Therefore, the enthalpy change is a positive value, and the reaction is not spontaneous. Therefore, 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, the sunlight supplies the required energy.
What are Exothermic Reactions?
An exothermic reaction is a process that releases energy to the surroundings, usually in the form of heat. In addition, energy may also release in other forms such as sound, light etc. Since the energy is released during the reaction, the products contain less energy than the reactants. Therefore, the enthalpy change (∆H) becomes negative.
In this type of reaction, energy releases 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 the reaction can sometimes be explosive. Exothermic reactions are spontaneous. An outside energy supply is not necessary for exothermic reactions since they produce the required energy as the reaction proceeds. However, to start the reaction, an initial energy supply may be necessary.
If we can capture this released energy, we can use it for a lot of useful work. For example, the energy released from the combustion of fuels is useful in operating a vehicle or a machine. Moreover, all combustion reactions are exothermic.
What is the Difference Between Endothermic and Exothermic Reactions?
Endothermic and exothermic are terms related to heat transfer in thermodynamic systems. The key difference between endothermic and exothermic reactions is that endothermic reactions absorb energy from the surrounding environment, whereas exothermic reactions release energy to the surrounding environment. Furthermore, the enthalpy change in an endothermic process is positive while the enthalpy change in an exothermic process is negative. When considering the final product, the product of endothermic reaction has higher energy compared to the energy of the reactants whereas, in exothermic reactions, the products have lower energy than reactants’ energy.
Summary – Endothermic vs Exothermic Reactions
Endothermic and exothermic are terms related to heat transfer in thermodynamic systems. The key difference between endothermic and exothermic reactions is that endothermic reactions absorb energy from the surrounding environment, whereas exothermic reactions release energy to the surrounding environment.
Reference:
Helmenstine, Anne Marie. “Endothermic Reaction Examples.” ThoughtCo, May. 9, 2019, Available here.
Image Courtesy:
1. “Endothermic Reaction” By Brazosport College – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Exothermic Reaction” By Brazosport College – Own work (CC BY-SA 3.0) via Commons Wikimedia