What happens to water molecules when water heats up?

• A. They slow down and clump together
• B. They speed up and move apart
• C. They freeze into solids
• D. They evaporate immediately

Answer: (B)

When water heats up, the energy from the heat causes the water molecules to move faster. As the temperature of the water increases, the kinetic energy of the molecules also increases, leading to more vigorous movement. This increased speed causes the molecules to move further apart from each other, transitioning from a more condensed state to a more spread-out state. This behavior is characteristic of liquids, where heat typically results in expansion. The molecules no longer remain tightly held together and can also facilitate processes like evaporation, but the immediate effect is the increase in speed and the distance between the molecules.

In contrast, slowing down and clumping together would occur when water cools, while freezing into solids happens at lower temperatures. Immediate evaporation doesn't capture the full process of heating either, as it implies a rapid transition without acknowledging the gradual increase in molecular movement and spacing.