Melt 1.5 kg of ice at 0 C. With L = 334 kJ/kg, how much heat is required?

• A. 501 kJ
• B. 668 kJ
• C. 334 kJ
• D. 1002 kJ

Answer: (B)

The key idea is latent heat of fusion—the energy required to change a solid into a liquid at the same temperature. The heat needed is Q = mL, where m is the mass and L is the latent heat per unit mass. Here. m = 1.5 kg and L = 334 kJ/kg, so Q = 1.5 × 334 = 501 kJ. So about 501 kJ of heat is needed to melt 1.5 kg of ice at 0 °C. The other numbers would correspond to melting different amounts of ice (for example, 334 kJ would melt 1 kg, 668 kJ would melt 2 kg, and 1002 kJ would melt 3 kg).