4. What effect does the reduction of the external pressure have on the boiling point? 5. As the temperature of a liquid increases, its vapor pressure increases. The boiling point of a liquid is the temperature at which the vapor pressure equals the external (atmospheric) pressure. a. Look up the Principles of Kinetic Molecular Theory of Matter. Use those principles and the concept of intermolecular forces to explain why the entire remaining sample of a liquid does not vaporize instantly as soon as the boiling point is reached. As part of your explanation, describe how an individual molecule moves from the liquid phase to the gas phase