Which statement best describes latent heat?

• A. The heat change that occurs without a temperature change during phase change
• B. The heat required to raise temperature by 1 degree
• C. The heat doing mechanical work
• D. The heat due to friction

Answer: (A)

Latent heat is the energy absorbed or released by a substance when it changes phase at a constant temperature. During melting or vaporization, the added heat goes into breaking intermolecular bonds rather than raising the temperature, so the temperature remains the same until the phase change finishes. For example, ice at 0°C needs latent heat of fusion to melt into liquid water, and liquid water at 100°C needs latent heat of vaporization to become steam. The other descriptions refer to sensible heat (temperature rise per degree), work done by the system, or heat from friction, none of which describe latent heat.