Question

Liquid hexane (bp:) is placed in a closed container at room temperature. At first, the pressure of the vapour phase increases, but after a short time, it stops changing. Why?

Short answer

The vapour pressure of the system with liquid hexane first increases because the process of vaporization starts taking place and after some time it becomes constant as the system attains equilibrium.

Step-by-step solution

Vapor Pressure

Liquid hexane with b.p. was placed in a closed container at room temperature. Initially, as the vaporization process initiates, the vapour pressure of the container increases. The process for liquid hexane at room temperature is denoted below:

$\mathbf{vaporization}\mathbf{\leftrightarrow }\mathbf{condensation}$

Rate of the two processes

After some time, as the equilibrium reaches the rate of vaporization gets equal to the rate of condensation, thus, no change in vapour pressure was noted.