Final answer:
Water's entropy decreases when it freezes as its molecules become more organized in a crystalline structure. The release of heat into the surroundings increases their entropy, ensuring the second law of thermodynamics is not violated. For ice melting, the entropy of the system increases as the solid turns into a more disordered liquid.
Step-by-step explanation:
When water freezes, the entropy of the water decreases. Entropy is a measure of the disorder or randomness of a system, and when water transitions from liquid to solid (freezes), its molecules become more ordered within the crystalline structure of ice. However, this does not violate the second law of thermodynamics, because the entropy of the surroundings increases. Specifically, as water releases heat during freezing, the released heat increases the entropy of the surroundings. Therefore, the total entropy of the universe increases, which is consistent with the second law of thermodynamics.
Considering ice melting, the opposite process of freezing, the entropy also changes. When ice melts into water, this represents a transition from a highly ordered solid structure to a disordered liquid state. The entropy of the system increases due to the increase in disorder of the water molecules as the solid lattice structure breaks down and they move more freely in the liquid state.