The enthalpy change when g of phenol dissolves in g of is given below at a certain temperature:<br>, — Thermodynamics and Thermochemistry Chemistry Question
Question
The enthalpy change when $x$ g of phenol dissolves in $y$ g of $\text{CHCl}_3$ is given below at a certain temperature:<br>$x = 0.632$, $y = 135.9$, $\Delta H\text{ (kcal)} = -0.021$<br>$x = 1.569$, $y = 148.69$, $\Delta H\text{ (kcal)} = -0.041$<br>Calculate the enthalpy of dilution per mole of phenol, when the second solution is diluted to the concentration of the first by addition of $\text{CHCl}_3$.
💡 Solution & Explanation
State 1: Moles phenol $n_1 = 0.632/94 = 0.00672$. $\Delta H_{sol,1} = -0.021 / 0.00672 = -3.123\text{ kcal/mol}$. State 2: Moles phenol $n_2 = 1.569/94 = 0.01669$. $\Delta H_{sol,2} = -0.041 / 0.01669 = -2.456\text{ kcal/mol}$. Diluting from State 2 to State 1 equates to $\Delta H_{dil} = \Delta H_{sol,1} - \Delta H_{sol,2} = -3.123 - (-2.456) = -0.667\text{ kcal/mol}$.