As water is heated, what happens to the molecules in the water?

• A. The molecules move faster and their kinetic energy increases.
• B. The molecules undergo a chemical change and form new substances.
• C. The molecules lose energy and slow down.
• D. The molecules decrease in size and move closer together.

Answer: (A)

Verified step by step guidance

1. Understand that heating water involves adding thermal energy to the system, which affects the motion of the water molecules.
2. Recall that temperature is a measure of the average kinetic energy of molecules in a substance, so increasing temperature means increasing molecular kinetic energy.
3. Recognize that as water is heated, the molecules gain kinetic energy, causing them to move faster and vibrate more vigorously.
4. Note that this process is a physical change, not a chemical change, so the molecules do not form new substances or change their chemical identity.
5. Conclude that the correct description is that the molecules move faster and their kinetic energy increases as water is heated.