Which formula computes the energy required to melt a mass m of ice at 0°C?

Study for the Cambridge Science – States of Matter Test. Prepare with flashcards and multiple choice questions, with hints and explanations for each question. Ready yourself for your exam!

Multiple Choice

Which formula computes the energy required to melt a mass m of ice at 0°C?

Explanation:
At 0°C, ice is at its melting point, so turning solid ice into liquid water requires only the latent heat of fusion. The energy needed per unit mass is Lf, the latent heat of fusion, so the total energy is Q = m × Lf. This is because the temperature doesn’t change during melting, so there’s no need to add any sensible heating term (Cp × ΔT) and no vaporization energy (Lv) is involved. Adding Lf + Lv would correspond to melting and then vaporizing, which isn’t required for melting alone. The correct expression captures just the energy to overcome the intermolecular forces holding the ice in the solid state at that temperature.

At 0°C, ice is at its melting point, so turning solid ice into liquid water requires only the latent heat of fusion. The energy needed per unit mass is Lf, the latent heat of fusion, so the total energy is Q = m × Lf. This is because the temperature doesn’t change during melting, so there’s no need to add any sensible heating term (Cp × ΔT) and no vaporization energy (Lv) is involved. Adding Lf + Lv would correspond to melting and then vaporizing, which isn’t required for melting alone. The correct expression captures just the energy to overcome the intermolecular forces holding the ice in the solid state at that temperature.

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