Suppose that a substance in a beaker is heated over a burner in a science lab. Which observation would most likely indicate that a chemical change has occurred in the substance? If the substance is a liquid or solid, an increase in temperature would indicate a chemical change.
If the substance is a liquid, a change of some of the liquid to gaseous form would indicate a chemical change.
If the substance is a solid, a change of some of the solid to liquid form would indicate a chemical change.
If the substance is a liquid or solid, production of an odor would indicate a chemical change.

Vander waals forces are inter molecular bonds that exist within molecules of the same substance. a water molecule is made up of oxygen and hydrogen atoms which share electrons between each other. the vander waals forces are forces that exist between multitude of different  molecules of water. dipole dipole forces is the type of vander waals force that exist in water. the oxygen atom which is more electronegative pulls the shared electron closer to itself thus generating a partial negative charge while the hydrogen acquire a partial positive charge. these two different charges causes attraction to occur in water molecules.