Question

When you heat the water in a pot, it boils. What do you infer from the above observation?
A) Heat is a form of energy
B) Water can boil itself
C) Water develops heat on its own
D) None of the above

Answer 1

Hint: Before approaching this question we need to understand the mechanism of boiling of water. Also remember that boiling of water and evaporation of water are two different things.

Complete step by step solution:
First let us understand the mechanism of boiling of water.
Water when it reaches the temperature of its boiling point or above its boiling point starts boiling. Boiling point is known as the temperature at which the vapour pressure of the liquid and the atmospheric pressure are the same. At this temperature, the water changes from liquid state to vapour state. For water the boiling point is at ${100^ \circ }C$ or $373K$ .
When water reaches ${100^ \circ }C$ the molecules of the liquid start moving very rapidly and have a lot of energy. This large amount of energy makes it difficult for the molecules to stay together in the form of liquid.

At ${100^ \circ }C$ the temperature of the water does not increase, the increased temperature is taken in the form of latent heat of evaporation by the water to convert its molecules from liquid to vapour. Latent means hidden energy.
Increase in temperature of the pot increases the heat provided to the pot. This heat is absorbed by the water to convert from liquid to vapour. But the liquid can only absorb energy to convert to liquid. Hence, we can say that heat is a form of energy and helps in converting the liquid to vapour.
The water cannot boil itself as it needs extra energy so the molecules more rapidly and convert to vapour. And this extra energy can be absorbed by water in the form of heat from outside.

Thus, option (A) Heat is a form of energy, is the correct option.

Note: Heat energy is also known as thermal energy. Energy can be in many forms such as mechanical energy, thermal energy, nuclear energy, chemical energy, electromagnetic energy, kinetic and potential energy. Remember that evaporation occurs only at the surface of the liquid whereas boiling occurs on the surface as well as inside the liquid.