Question

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

1. adding salt to water
2. decreasing the temperature of water
3. decreasing the volume of the vessel to one-third
4. decreasing the quantity of water

• A. 3, 4
• B. 2 only
• C. All
• D. 1, 2

Answer 1

Answer:

D. 1, 2

1. Adding salt to water: When salt is added to water, it lowers the vapor pressure of the solution. This is because the salt dissolves into ions, which occupy some of the space at the surface of the water, making it harder for water molecules to escape into the vapor phase.

2. Decreasing the temperature of water: As the temperature of water decreases, the kinetic energy of the water molecules also decreases. This reduces the rate at which water molecules escape into the vapor phase, resulting in a decrease in vapor pressure.

Both of these changes will decrease the vapor pressure of water in a sealed vessel!