Question

Which of the following is correct for the solution showing positive deviations from Raoult's law?

• A. $\mathrm{dV}=+\mathrm{ve}\mathrm{and}\mathrm{dH}=+\mathrm{ve}$
• B. $\mathrm{dV}=+\mathrm{ve}\mathrm{and}\mathrm{dH}=-\mathrm{ve}$
• C. $\mathrm{dV}=-\mathrm{ve}\mathrm{and}\mathrm{dH}=+\mathrm{ve}$
• D. $\mathrm{dV}=-\mathrm{ve}\mathrm{and}\mathrm{dH}=-\mathrm{ve}$

Answer 1

The correct option is A

$\mathrm{dV}=+\mathrm{ve}\mathrm{and}\mathrm{dH}=+\mathrm{ve}$

The explanation for the correct answer (a)

• Explanation: If a solution differs from Raoult's law in a positive way both its $\mathrm{dV}$ and $\mathrm{dH}$ will be positive. Most alcoholic solutions have positive deviations.
• The positive deviation is caused by the energy-intensive breakdown of hydrogen bonds.

The explanation for the incorrect answer

(b)

• Explanation: Raoult's law states that the vapor pressure of a solution containing a nonvolatile solute is directly proportional to the mole fraction.
• At a given temperature, the solvent in non-perfect solutions exhibits both positive and negative departures from ideal behavior.

(c)

• Explanation: If the solutions have a negative deviation, the negative-positive deviations dV and dH will be negative-positive deviations, which are commonly seen when a solution contains alcohol.

(d)

• Explanation: $\mathrm{dV}$ and $\mathrm{dH}$ will be negative if the solutions have a negative deviation.
• Acidic solutions usually show negative deviations Negative deviations result from the release of energy by hydrogen bonds in the solution.

The correct option is (a): If a solution differs from Raoult's law in a positive way, both its $\mathrm{dV}$ and $\mathrm{dH}$ will be positive alcoholic solutions usually show positive deviations the breakdown of hydrogen bonds which requires energy causes positive deviation.