when add a non-volatile impurity, it is usually something in the form of a solid or liquid and will create bonds with the molecule already present in the mixture to be added. The new bonds can either be stronger or weaker, depending on the size of the new molecules and the type of bonding. In some cases, stronger bonding is achieved and to make the new mixture change its physical state from liquid to gas, more energy is required to break apart these bonds and allow the molecules to move freely. Thus, this increase in required energy is represented by the increased boiling point.