Vapour pressures of water, acetone and ethanol at 293K are 2.34kPa, 12.36kPa and 5.85 kPa respectively. Which of these has the lowest and the highest boiling point? At 293K which of these evaporates least in a sealed container before equilibrium is established?

Solution

We know that when the temperature increases, the vapour pressure of a liquid also increases and at the boiling point, vapour pressure becomes equal to the atmospheric pressure. A liquid with lower vapour pressure will require a higher temperature for it to attain its vapour pressure equal to the atmospheric pressure. Therefore, the liquid with the highest vapour pressure will have the lowest boiling point. Acetone has the lowest boiling point and water has the highest boiling point.
At 293K, water evaporates least in the sealed container before equilibrium is established.