1. Consider the following two substances and their vapor pressures at 298 K.
Substance Vapor Pressure (mmHg)
Based on this information compare the characteristcs of the two substances.
weaker intermolecular force
higher boiling point
higher heat of vaporization
exist in gaseous phase at 300 K
2. The vapor pressure of dichloromethane, CH 2Cl2, at 0°C is 134 mmHg. The normal boiling point of dichloromethane is 40. Calculate its molar heat of vaporization?
1. Substance A has a lower vapor pressure than substance B. A lower vapor pressure means stronger intermolecular forces because the liquid molecules do not easily escape to the gaseous phase. Therefore, substance A has a stronger intermolecular force and substance B has a weaker intermolecular force.
Since Substance A has a stronger intermolecular force, it also has a higher boiling point and higher heat of vaporization. This is because more energy (in the form of heat) is needed to bring the liquid to boil and to vaporize the liquid.