Final answer:
The average kinetic energy of water molecules increases when liquid water's temperature rises from 10°C to 20°C, indicating greater molecular motion and energy.
Step-by-step explanation:
The average kinetic energy of water molecules increases when H₂O(l) at 10°C changes to H₂O(l) at 20°C. This is because kinetic energy is directly related to temperature, and an increase in temperature from 10°C to 20°C reflects a rise in the motion and energy of the water molecules.
When ice (H₂O(s)) changes to liquid water (H₂O(l)) at 0°C, despite energy being absorbed, the temperature remains at 0°C until all the ice has melted. The temperature of water does not increase during a phase change; instead, energy goes into breaking hydrogen bonds. Similarly, when liquid water cools (H₂O(l) at 20°C changes to H₂O(l) at 10°C), the average kinetic energy of water molecules decreases as the temperature drops.