Calculate the heat energy lost when 10g of boiling water changes to ice at 0°C. [Specific latent heat of ice…

Analyze the question: Boiling water (100°C) must lose heat in two stages to become ice at 0°C:

1. Cooling the water from 100°C to 0°C
2. Freezing the water at 0°C into ice (releasing latent heat)

Concept:

• Heat lost in cooling: Q₁ = mcΔθ
• Heat lost in freezing: Q₂ = mL
• Total heat lost = Q₁ + Q₂

Solution:

Given: m = 10 g, c = 4.2 J g⁻¹ K⁻¹, L = 336 J g⁻¹, Δθ = 100 − 0 = 100 K

Stage 1 (cooling the water): Q₁ = 10 × 4.2 × 100 = 4200 J

Stage 2 (freezing at 0°C): Q₂ = 10 × 336 = 3360 J

Total: Q = 4200 + 3360 = 7560 J

Answer: 7560 J, which is option E.

Tip: When a question says "boiling water" it means a starting temperature of 100°C. Whenever a substance changes state and also changes temperature, work out each stage separately (the temperature change with mcΔθ, the state change with mL) and add them. Students who pick B or D have forgotten one of the two stages.