Chemistry - Thermochemistry Question with Solution | TestHub
The enthalpy change when x g of phenol dissolves in y g of CHCl3 is given below at a certain temperature:
x = 0.632, y = 135.9, ΔH = -0.021 kcal
x = 1.569, y = 148.69, ΔH = -0.041 kcal
Calculate the enthalpy of dilution per mole of phenol, when the second solution is diluted to the concentration of the first by addition of CHCl3.
Options:
Answer:
Solution:
First, calculate the moles of phenol (molar mass M = 94 g/mol) for each solution:
For solution 1:
Moles of phenol = 0.632 g/(94 g/mol) = 0.00672 mol
The enthalpy of solution for solution 1, Δ Hsoln,1, is:
Δ Hsoln,1 = (-0.021 kcal)/0.00672 mol = -3.12 kcal/mol
For solution 2:
Moles of phenol = 1.569 g/(94 g/mol) = 0.01669 mol
The enthalpy of solution for solution 2, Δ Hsoln,2, is:
Δ Hsoln,2 = (-0.041 kcal)/0.01669 mol = -2.46 kcal/mol
Next, calculate the enthalpy of dilution, Δ Hdil, which represents the enthalpy change when solution 2 is diluted to the concentration of solution 1:
Δ Hdil = Δ Hsoln,1 - Δ Hsoln,2
Δ Hdil = -3.12 kcal/mol - (-2.46 kcal/mol) = -0.67 kcal/mol
This corresponds to option (b).
