NEET
- Exam
- NEET
- Subject
- Physics
- Chapter
- Thermodynamics
NEET · Physics · Thermodynamics
Given below are two statements: one is labelled as Assertion (A)...
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Evaporation has a cooling effect.
Reason (R) : At the surface of liquid, some of the faster upward moving molecules have enough kinetic energy to overcome the attraction from other molecules and escape from the liquid. With these faster molecules the average kinetic energy left behind is reduced.
In the light of the above statements, choose the most appropriate answer from the options given below:
Options
- ABoth (A) and (R) are true and (R) is the correct explanation of (A).
- BBoth (A) and (R) are true and (R) is NOT the correct explanation of (A).
- C(A) is true but (R) is false.
- D(A) is false but (R) is true.
Correct answer
A. Both (A) and (R) are true and (R) is the correct explanation of (A).
Step-by-step solution
The correct option is A Statement 1 and statement 2 both are correct and statement 2 is the correct explanation of statement 1.
When a liquid is placed in an open vessel, its molecules constantly move in different directions with different velocities. Thus, as these molecules are moving at different speeds, they possess different kinetic energies. At any particular temperature, the energies of some surface molecules may be higher so that they can overcome the forces of attraction of the neighboring molecules and can leave the liquid and come above the surface of the liquid. This process is called evaporation. Evaporation is a spontaneous process. It occurs spontaneously at all temperatures. During evaporation, the surface molecules with high kinetic energy leave the liquid and come above the surface of the liquid. The molecules remaining in the liquid state have lesser energy and hence the temperature reduces. This is the reason why evaporation causes cooling. Therefore, statement 1 and 2 both are correct and statement 2 is the correct explanation of statement 1.