Question

(i) What are Exothermic and Endothermic reactions? Explain with example.

Hint:

In exothermic reactions, energy is released (feels warm), while in endothermic reactions, energy is absorbed (feels cool).

Answer 1

Exothermic Reactions:
Exothermic reactions are chemical reactions in which energy is released in the form of heat or light. These reactions result in a net release of energy because the energy required to break the bonds of reactants is less than the energy released when new bonds are formed in the products. Exothermic reactions usually cause an increase in temperature. Example:
A common example of an exothermic reaction is the combustion of fuels. For example, when wood burns in the presence of oxygen: \[ \text{C}_6\text{H}_6 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{Heat} \] This reaction releases heat and light as energy. Endothermic Reactions:
Endothermic reactions are chemical reactions that absorb energy from their surroundings in the form of heat. These reactions require more energy to break bonds in the reactants than is released when new bonds are formed in the products, resulting in a net absorption of energy. Endothermic reactions usually cause a decrease in temperature. Example:
An example of an endothermic reaction is the process of photosynthesis in plants, where energy is absorbed from sunlight: \[ \text{6CO}_2 + \text{6H}_2\text{O} + \text{Energy (sunlight)} \rightarrow \text{C}_6\text{H}_12\text{O}_6 + \text{6O}_2 \] Here, the energy from sunlight is absorbed to convert carbon dioxide and water into glucose. Conclusion:
Exothermic reactions release energy, while endothermic reactions absorb energy. These reactions are fundamental to many processes in nature and industrial applications.