Question

Evaporation of water is:
A. a process in which neither heat is evolved nor absorbed
B. a process accompanied by chemical reaction
C. an exothermic change
D. an endothermic change

Answer 1

Hint:Evaporation is a process in which water changes from liquid to vapour phase. External energy is required to bring the phase transition.

Complete answer:Evaporation of water is referred to as the movement of water molecules from liquid phase to vapour phase. The process is carried out by applying heat from an external source. By absorbing the heat energy the molecules of water get excited and undergo phase transition from liquid phase to gaseous phase.
The evaporation of water is also known as vaporization. In this process the water is raised to a temperature of \[373K\]. The molecules of water in liquid state undergo collision with each other and the absorbed energy is transferred to each other.
When the molecules at the surface of water absorb enough energy to overcome the vapour pressure above it the molecules are released or escape from the surface. The energy released after evaporation of liquids leads to reduction in temperature of the remaining liquid which results in evaporative cooling.
The process is continued until equilibrium is reached between the vapour phase and the liquid phase. At this point the rate of evaporation of liquid is equal to the rate of condensation. Evaporation does not occur with the whole amount of liquid at a time rather it occurs in fractions. The fraction depends on the number of molecules which reside at the surface and has enough energy.
Thus option D is correct i.e. evaporation of water is an endothermic change as energy is absorbed by the water molecules.
Options A, B and C are incorrect as heat is absorbed in evaporation, it is not a chemical reaction and it is not an exothermic change.

Note:Unlike the endothermic system in which heat is absorbed, in the exothermic system heat is evolved. The melting of ice is also an endothermic process as heat is absorbed by the solid phase to change into liquid phase.