Final answer:
Water transitions from solid to liquid to gas by gaining kinetic energy, which increases particle motion and system entropy. These changes are physical, meaning while the arrangement and energy of H2O molecules change, their chemical structure does not.
Step-by-step explanation:
State Change of Water and Particle Motion
In an experiment where water changes state, we can examine these changes through the lens of the kinetic molecular theory (KMT). When water transitions from ice (solid) to liquid water, and then to water vapor (gas), what is essentially changing is the amount of kinetic energy the water molecules possess. In the solid state, water molecules are closely packed with limited movement, representing low kinetic energy. As heat is applied, energy is absorbed and the molecules begin to move more freely, which is indicative of the melting process. Once the liquid state is reached, the molecules have more energy and are able to move past each other easily, but still stay relatively close. Upon further heating to the boiling point, the molecules have sufficient energy to overcome intermolecular forces and spread apart, becoming water vapor.
During the melting process, energy is transferred to the ice, increasing the molecular motion and entropy of the system. This energy predominantly comes from the surroundings or a direct heat source. Entropy is a measure of disorder within a system, and during the melting and vaporization processes, entropy increases as the water molecules move from a more ordered (solid) to a less ordered (liquid and gas) state.
These changes are examples of physical changes, where water molecules rearrange without breaking chemical bonds. Hence, in all state changes from solid to liquid to gas, the intrinsic molecular structure of water remains the same - H2O. It is the amount of kinetic energy and the freedom of movement that differ between the states.