Though you add heat, the temperature of boiling water remains constant because ...

• A. the water molecules stop moving once boiling begins
• B. the heat is immediately lost to the surroundings
• C. the added energy is used to break intermolecular forces during the phase change
• D. the boiling point decreases as more heat is added

Answer: (C)

Verified step by step guidance

1. Understand that during a phase change, such as boiling, the temperature of a substance remains constant even though heat is being added.
2. Recognize that the heat added during boiling is called the latent heat of vaporization, which is the energy required to convert liquid water into vapor without changing temperature.
3. Know that this energy is used to overcome the intermolecular forces (like hydrogen bonds) holding the water molecules together in the liquid phase.
4. Realize that because the energy goes into breaking these intermolecular forces rather than increasing kinetic energy, the temperature does not rise during boiling.
5. Conclude that the correct explanation is that the added energy is used to break intermolecular forces during the phase change, not to increase the temperature.