Question

Putting a lid on a boiling pot greatly reduces the heat transfer necessary to keep it boiling. Explain why.

Short answer

A lid on a boiling pot makes condensation of vapor molecules that are formed from boiling and releases energy, which helps to reduce the heat transfer required for boiling.

Step-by-step solution

Explain what happens while putting a lid on a boiling pot

Lids are commonly used in cooking to increase the efficiency of boiling or to keep boiling for a longer time. At the boiling point, water molecules in the pot turn into vapor, and it will escape into the surrounding atmosphere. But if the pot is covered with a lid, the vapor molecules remain at the lid, and this leads to a reduction in the amount of heat transfer.

Explain how a lid reduces the heat transfer in the boiling pot

The water vapor remaining on the lid will again turn into water. The boiling point of water is the same as that of the condensation point. So, the amount of water that turns to vapor and the amount of vapor that condenses to water will be the same. So, the boiling process continues for a longer time.

During evaporation, more heat is required. So, if we are using the boiling pot without a lid, more energy will be required. But while using the lid, the evaporated water molecules condensed back to water by releasing energy. So, the lid reduces heat transfer.

Thus, the lid on the boiling pot reduces heat transfer by catching the evaporated water molecules.