Question

Why is vaporization endothermic? Why is condensation exothermic?

Answer 1

Hint: The change of state from liquid to gas is known as vaporization and the conversion of vapor state into liquid state is known as condensation. The temperature of vaporization is 373K for water. In water conversion of liquid water to vapor is vaporization and vapor to water is condensation.

Complete answer:
Endothermic process is the process in which the heat is absorbed. Let us consider the endothermic process of conversion of ice to water and then to water vapor. To convert one state to another we need to break the bonds between molecules. The breaking of bonds will absorb energy and forming of bonds will release energy. To form gas from solid, a high amount of energy is required to break the bonds between molecules of water, and to overcome the vapor pressure to form vapor. Hence, vaporization is an exothermic process.
Exothermic reaction is the process in which the heat is evolved. Consider the exothermic process of conversion of water vapor to liquid water. The molecules in gas state are higher in energy than the molecules in liquid state. From gas to liquid is a conversion of high energy to low energy state. The molecules of gas have to release a large amount of Kinetic energy to slow down their molecules and form temporary bonds to become a liquid. This energy is released in the surroundings. Thus, condensation is an exothermic reaction.

Note:
Exothermic reaction is a reaction in which the energy of the reactants is lower than that of the products. Whereas, endothermic reaction is a reaction in which the energy of the reactants is higher than that of products. The reactants are converted to a lower energy state from a higher energy state.