Final answer:
In order for water to change from a solid to a liquid to a gas, the attractive forces between the water molecules must be overcome.
Step-by-step explanation:
When water changes from solid to liquid to gas, the attractive forces between the water molecules must be overcome.
In the solid phase, water molecules are held together by intermolecular forces, such as hydrogen bonds. These forces must be partially broken in order for the water to change into a liquid.
Similarly, in the liquid phase, the water molecules are still attracted to each other by intermolecular forces. To change from liquid to gas, these forces must be completely overcome.