The specific heat capacity of liquid water is about 4.18 kJ/(kg·K). How much energy is needed to raise 1 kg of water by 1°C?

• A. 0.418 kJ
• B. 4.18 kJ
• C. 41.8 kJ
• D. 418 kJ

Answer: (B)

The question hinges on using the specific heat concept and the energy balance Q = m c ΔT. Specific heat capacity tells us how much energy is needed to raise the temperature of a unit mass by one degree. For water, c ≈ 4.18 kJ/(kg·K). The energy to heat a mass m by a temperature change ΔT is Q = m c ΔT. Here m = 1 kg and ΔT = 1 K (1°C is the same size change as 1 K). So Q = 1 × 4.18 × 1 = 4.18 kJ.

Thus, about 4.18 kJ of energy is needed. If either the mass or the temperature change were different, the energy would scale accordingly (e.g., more mass or a larger ΔT requires more energy).