Q73 / 200 · NEET 2003 · Chemistry
Formation of a solution from two components can be considered as:
(i) Pure solvent $\rightarrow$ separated solvent molecules $\Delta \mathrm{H}_1$
(ii) Pure solute $\rightarrow$ separated solute molecules, $\Delta \mathrm{H}_2$
(iii) Separated solvent and solute molecules $\rightarrow$ solution, $\Delta \mathrm{H}_3$
Solution so formed will be ideal of:
- Correct answerA$\Delta \mathrm{H}_{\text {soln }}=\Delta \mathrm{H}_1+\Delta \mathrm{H}_2+\Delta \mathrm{H}_3$
- B$\Delta \mathrm{H}_{\text {soln }}=\Delta \mathrm{H}_1+\Delta \mathrm{H}_2-\Delta \mathrm{H}_3$
- C$\Delta \mathrm{H}_{\text {soln }}=\Delta \mathrm{H}_1-\Delta \mathrm{H}_2-\Delta \mathrm{H}_3$
- D$\mathrm{AH}_{\text {soln }}=\mathrm{AH}_3-\mathrm{AH}_1-\mathrm{AH}_2$
Solution
So the enthalpy of solution can either be endothermic, exothermic or neither $(\Delta$ Hsolution $=0)$, depending on how much heat is required or release in each step. If $\Delta$ Hsolution $=$ 0 , then the solution is called an ideal solution and if
$\Delta$ Hsolution $>0$ or $\Delta$ Hsolution $< 0$, then these solutions are called non-ideal solutions.
Related Theory
The enthalpy of solution depends on the strengths of intermolecular forces of the solute and solvent. If the solution is ideal, and $\Delta \mathrm{H}$ solution $=0$, then
$\begin{aligned}
& \Delta H_{\text {solution }}=\Delta H_1+\Delta H_2+\Delta H_3=0 \\
& \Delta H_1+\Delta H_2=-\Delta H_3
\end{aligned}$
Hence, the correct answer is option: 'A'.