Question

Temperatures of liquids A,B,C,D are 25,50,75,90 (${}^{0}C$) respectively. Order of their vapour pressures is:

• A. A
• B. B
• C. C
• D. D

Answer 1

The vapour pressure of a liquid at any temperature is defined as the pressure exerted by the vapour in equilibrium with the liquid at that temperature.

$\Rightarrow$ More molecules in vapour phase lead to more vapour pressure.

$\Rightarrow$ At higher temperature, more number of molecules escape into vapour phase.

Therefore, as temperature increases, the vapour pressure increases because at higher temperatures, large number of molecules escape into the vapour phase.

Since A<B<C<D is the order of temperatures, order of vapour pressures would be A<B<C<D.