Question

Is condensing water vapor an exothermic or an endothermic process?

Answer 1

Hint: We must know that endothermic processes are the process which require an input of energy to proceed and are signified by a positive change in enthalpy whereas the exothermic processes are the process which release energy upon completion and are signified by a negative enthalpy change.

Complete answer:
Let us first discuss how energy is stored in a water vapour. Molecules may have different amounts and types of kinetic energy i.e., vibrational and rotational kinetic energy. These vibrational and rotational kinetic energy manifest themselves when molecules tend to show rotation or are bent. The energy in water vapor is translational kinetic energy which is independent of temperature. As temperature decreases, the temperature is dissipated in the form of heat and eventually the intermolecular bonds of molecules become strong enough to change the state from vapor to liquid.
Now, condensation is the process in which the vapours of water turn into liquid water molecules. This basically occurs when molecules of water vapour come in contact with cooler molecules and due to which it loses some of its energy in the form of heat and transforms its state into liquid.
Therefore, we can conclude that as the molecules of water vapour condenses into liquid, it loses energy in the form of heat and thus, the process is an exothermic process.

Note:
It is important to note that when molecules of water vapour transform from liquid phase to gaseous phase, the amount of energy required is termed as enthalpy of vaporization. In order to reverse this process i.e., transforming molecules from gaseous phase to liquid phase, the amount of energy released is equal to the enthalpy of vaporization.