An ice cube has mass of 20 g at 5°C. Calculate the energy required to raise its temperature to 0°C. [Specific heat capacity of ice = 2.1 J/g°c]

Analyze the question: We need the heat energy needed to warm ice from one temperature to another. The ice is only being warmed, not melted, so we use the specific heat capacity formula.

Concept: Q = mcΔθ

where m is the mass, c is the specific heat capacity, and Δθ is the change in temperature.

Solution:

The question says the ice is at "5°C" and is raised to 0°C. Ice at +5°C isn't physically possible, since it would have melted. This is almost certainly a typo for -5°C, which is the usual form of this question. The temperature change is then:

Δθ = 0 − (−5) = 5°C

Substituting:

• m = 20 g
• c = 2.1 J/g°C
• Δθ = 5°C

Q = 20 × 2.1 × 5 Q = 42 × 5 Q = 210 J

Check against the options: 210 J matches option D.

Note on the typo: If you take the numbers literally (5°C to 0°C), the change is still 5 degrees in size, so the magnitude is the same, 210 J (the sign would just be negative, meaning heat is lost).

Tip: Watch for common slips. Option C (42 J) is what you get if you forget to multiply by the temperature change (20 × 2.1). Option A (105 J) comes from halving the answer by mistake. Always multiply all three quantities: m × c × Δθ.

Also remember that a change of phase (ice to water at 0°C) would need latent heat, Q = ml, but that isn't needed here because the question stops at 0°C.