The molar enthalpy of fusion of NaCl is

CHEMISTRY · Single correct · AP · Chemistry · Thermochemistry · Thermochemistry

Problem

30.2\,\text{kJ mol}^{-1}

. A student claims that freezing

3.0\,\text{mol}

of molten NaCl would absorb

90.6\,\text{kJ}

of heat. Which evaluation of this claim is most accurate? (a) The claim is incorrect; freezing would release

90.6\,\text{kJ}

, so the enthalpy change is

−90.6\,\text{kJ}

. (b) The claim is correct because energy is required to organize ions into a crystal lattice during freezing. (c) The claim is incorrect; only

30.2\,\text{kJ}

of heat would be absorbed when

3.0\,\text{mol}

of NaCl freezes. (d) The claim is incorrect because enthalpy change depends on temperature, not on the number of moles frozen.