at standard pressure, water has unusual properties that are due to both its molecular structure and intermolecular forces. for example, although most liquids contract when they freeze, water expands, making ice less dense than liquid water. water has a much higher boiling point than most other molecular compounds having a similar gram-formula mass. determine the total amount of heat, in joules, required to completely vaporize a 50.0-gram sample of h2o( ) at its boiling point at standard pressure.