Ncert Exercises & Solutions

Which of the following changes decrease the vapour pressure of water kept in a sealed vessel?

1. Decreasing the quantity of water

2. Adding salt to water

3. Decreasing the volume of the vessel to one-half

4. Decreasing the temperature of water

(b, d)

When salt is added, less surface area is available for the water molecules to vaporise because salt molecules occupy the position of water molecules on the surface. Hence, vapour pressure of the water decreases.

Moreover, vapour pressure also decreases with decrease in temperature because kinetic energy of the molecules decrease.

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