Final answer:
Water molecules increase in kinetic energy and become less restricted in their movement as they transition from solid to liquid to gas. This is due to the addition of heat, which causes the phase changes, each at specific temperatures like the melting and boiling points.
Step-by-step explanation:
The states of matter—solid, liquid, and gas—are distinguished by changes in the kinetic energy of water molecules. When water is in its solid state, ice, its molecules are tightly bound together in a structured lattice, exhibiting minimal movement and having low kinetic energy. As heat is added, the temperature and kinetic energy increase, allowing the molecules to move more freely, leading to a phase change to liquid water.
In the liquid state, the molecules have more kinetic energy than in the solid state, which allows them to flow and take the shape of their container while still maintaining close contact with each other. Upon further heating, when the temperature reaches the boiling point (100° C at standard atmospheric pressure), the molecules have enough kinetic energy to overcome intermolecular forces completely, transitioning to the gas phase where they are free to move independently of each other and fill the entire container.
In summary, as water changes from solid to liquid to gas, the average kinetic energy of its molecules increases. This causes them to move from being fixed in place, to sliding past one another, to moving independently at high speeds. The corresponding temperature changes reflect the amount of heat added or removed, leading to the different observable properties of the three states of matter.