The enthalpy change when x g of naphthalene (C 10 H 8 , molar mass 128 g/mol) dissolves in y g of CCl 4 is given below at a certain temperature: x = 0.640, y = 120.0, ΔH = +0.020 kcal x = 1.280, y = 1

Question

The enthalpy change when x g of naphthalene (C₁₀H₈, molar mass 128 g/mol) dissolves in y g of CCl₄ is given below at a certain temperature:

x = 0.640, y = 120.0, ΔH = +0.020 kcal

x = 1.280, y = 140.0, ΔH = +0.032 kcal

Calculate the enthalpy of dilution per mole of naphthalene, when the second solution is diluted to the concentration of the first by addition of CCl₄.

TestHub · Accepted Answer

Moles of naphthalene: solution 1: 0.640/128 = 0.005 mol, ΔH soln,1 = +0.020/0.005 = +4.00 kcal/mol; solution 2: 1.280/128 = 0.010 mol, ΔH soln,2 = +0.032/0.010 = +3.20 kcal/mol. Diluting solution 2 to the concentration of solution 1: ΔH dil = ΔH soln,1 - ΔH soln,2 = 4.00 - 3.20 = +0.80 kcal/mol. This is option (d).

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