Explain why an organic liquid vaporises at a temperature below its boiling point in steam distillation?

Explanation

In steam distillation, the organic liquid starts to boil when the sum of vapour pressure due to the organic liquid (`p_(1)`) and the vapour pressure due to water (`p_(2)`) becomes equal to atmospheric pressure (p), that is, p = `p_(1) + p_(2)`
Since `p_(1) lt p_(2)`, organic liquid will vapourise at a lower temperature than its boiling point.