Question

When water droplets merge to form a bigger drop 

(a) energy is liberated 

(b) energy is absorbed 

(c) energy is neither liberated nor absobred 

(d) energy may either be liberated or absorbed depending on the nature of the liquid.

Answer 1

(a) energy is liberated

Explanation: 

When water droplets merge to form a bigger drop the total surface area decreases. Since the molecules in the surface have greater potential energy, the potential energy of surface molecules in the bigger drop decreases from before the merger. In other terms, the surface energy per unit area is equal to the surface tension. Since the surface tension remains the same, the surface energy will be less in the merged bigger drop. Hence the energy is liberated in the process.