Question

Explain why organic liquid vapourises at a temperature below its boiling point in its steam distillation.

Answer 1

This is because in steam distillation ,it is the sum of the vapour pressure of organic liquid (p₁)and water (p₂)which becomes equal to the atmospheric pressure. While the vapour pressure of organic liquid is still lower than it's boiling point.
Actually
p = p₁ + p2
while p₁<p₂