Question

Why in a closed container, vapour pressure is not equal to atmospheric pressure?

Answer 1

There are two conditions in a closed container in general . One , there is a substance , say liquid in the container or it is empty. The empty container has same pressure as outside . But if the liquid is present , it forms vapours which in return increase the pressure inside container . The motion of vapour molecules hit the walls of container again and again as they gain energy from surroundings (assuming the walls are not adiabatic - adiabatic walls are those which do not let the energy escape out of container ) hence the vapour pressure inside the container is not equal to the pressure outside !!