According to this web article: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/phase.html#c6 "In the process of heating water from 0 to 100 C, 100 calories of energy must be added. Part of that energy increases the kinetic energy of the molecules, and some adds to the potential energy." "The net gain in kinetic energy is then 16.7 calories/gram when the water is heated from 0 to 100 C. The remainder of the energy goes into weakening the attractive forces between the water molecules. This weakening of the intermolecular forces manifests itself in the reduction of the surface tension of water as it is heated." Now by "weakening," I'm assuming the author means, on average, an increase in the intermolecular distance between water molecules in the liquid water. So why do have a discontinuous phase transition for water that's transitioning from liquid to gas? In my mind, what distinguishes liquid water from water vapor at the same temperature is said average intermolecular distance. But for reasons I cannot understand, by the time water is heated up to the supposed boiling point, there still remains a significant amount of average intermolecular distance to gain. So there has to be a large increase in potential energy. But couldn't the boiling point of water be defined another way so that the average intermolecular distance is just shy of what is classified as being water vapor's (assuming constant pressure) upon reaching said point? That way it would just be a continuous change, right? Please help me. Even if it means totally dismantling my presented assumptions.