Two crystalline solids melt at their respective melting points

CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics

Problem

Two crystalline solids melt at their respective melting points. • Substance A: ΔHfus=8.0 kJ mol−1\Delta H_{\text{fus}}=8.0\,\text{kJ\,mol}^{-1}, molar mass 32 g mol−132\,\text{g\,mol}^{-1} • Substance B: ΔHfus=6.0 kJ mol−1\Delta H_{\text{fus}}=6.0\,\text{kJ\,mol}^{-1}, molar mass 18 g mol−118\,\text{g\,mol}^{-1} Equal masses of 36 g36\,\text{g} of each substance are melted. Which statement correctly compares the total heat absorbed by the two samples? (a) Substance A absorbs more heat because its molar enthalpy of fusion is larger. (b) Substance A absorbs more heat because heat is calculated by multiplying ΔHfus\Delta H_{\text{fus}} directly by the mass in grams. (c) Substance B absorbs more heat because the 36 g sample contains more moles that must each absorb ΔHfus.\Delta H_{\text{fus}}. (d) Both samples absorb the same amount of heat because equal masses of each substance are melted.

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