Question

When vapour condenses into liquid:
A) It absorbs heat
B) It liberates heat
C) Its temperature increases
D) Its temperature decreases

Answer 1

Hint: Recall that the condensation is the process when the water changes from the gaseous form to the liquid form. This means that the state of water has changed from gas to liquid. The water molecules will be more organised in the liquid form. It is the change of physical state of matter.

Complete solution:
Now when the vapours are made to condense in a liquid form, then the intermolecular distance between the particles will decrease. This is because in condensation, as the vapours cool down and condense, they get attached to the small particles floating in the air. As a result they will be more closely placed to each other and form liquid droplets of small size. Therefore, less energy will be required to bind them together. This is because the change in state is occurring at the same temperature.
Since it is clear from the above discussion that less amount of energy is required to bind the molecules of a liquid than that of a vapour, so the remaining energy will be liberated or released as heat energy.

Option B is the right answer.

Note: It is important to remember that the reaction or the process in which the heat is liberated is also known as exothermic reactions. The word exothermic is a combination of two words- exo and thermic. ‘Exo’ means ‘outside’ and ‘thermic’ means ‘related to heat’. The exothermic change can be a physical or a chemical change.