Lattice energy of NaCl is −186 kcal/mol. If solution enthalpies of Na+ and Cl− are −97 kcal/mol and −85 kcal/mol respectively. The enthalpy NaCl solution in kcal will be:
A
−4
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B
182
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C
368
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D
4
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Solution
The correct option is D4 The enthalpy of solution of NaCl in kcal is:
ΔHsolution=ΔHsolution of cation+ΔHsolution of anion−ΔHLattice energy of NaCl
ΔHsolution=(−97)+(−85)−(−186)=4 kcal/mol
The enthalpy change of solution refers to the amount of heat that is released or absorbed during the dissolving process (at constant pressure). This enthalpy of solution (ΔHsolution) can either be positive (endothermic) or negative (exothermic).