Final answer:
The average kinetic energy of water molecules decreases when the temperature of the water decreases. Thus, among the options provided, option d) H₂O(l) at 337 K changes to H₂O(l) at 300 K is the scenario where the average kinetic energy of water molecules decreases. Option d is correct.
Step-by-step explanation:
The question asks when the average kinetic energy of water molecules decreases. The average kinetic energy of a substance is directly proportional to its temperature. Therefore, when the temperature of water decreases, the average kinetic energy of its molecules also decreases.
Looking at the options provided:
a) H₂O(l) at 373 K changes to H₂O(g) at 373 K - During this phase change, the temperature is constant because the energy goes into changing the state from liquid to gas, not into increasing kinetic energy.
b) H₂O(s) at 273 K changes to H₂O(l) at 273 K - This is a phase change from solid to liquid at the same temperature, so the average kinetic energy does not decrease.
c) H₂O(s) at 200 K changes to H₂O(s) at 237 K - Here, the temperature increases, so the average kinetic energy increases, not decreases.
d) H₂O(l) at 337 K changes to H₂O(l) at 300 K - The temperature of the water decreases in this scenario, resulting in a decrease in the average kinetic energy of the water molecules.
Therefore, the average kinetic energy of water molecules decreases in option d) H₂O(l) at 337 K changes to H₂O(l) at 300 K.