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Solutions — Chemistry STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceChemistrySolutions3 Marks
Question
State Raoult’s law for a solution containing volatile components. How does Raoult’s law become a special case of Henry’s law?
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Answer

For a solution of volatile liquids, Raoult’s law states that the partial vapour pressure of each component of the solution is directly proportional to its mole fraction present in solution, i.e., $\text{P}_\text{A}\propto\text{x}_\text{A},\ \text{or }\text{P}_{\text{A}}=\text{P}_\text{A}^0\text{x}_\text{A}$
According to Henry’s law, the partial pressure of a gas in vapour phase $(p)$ is directly proportional to mole fraction $(x)$ of the gas in the solution.
$p = K_Hx$ On comparing it with Raoult’s law it can be seen that partial pressure of the volatile component or gas is directly proportional to its mole fraction in solution,
only the proportionality constant $K_H$ differs from $\text{P}_\text{A}^0,$
$\text{p}_\text{A}\propto\text{x}$
Thus, it becomes a special case of Henry's law in which $\text{K}_\text{H}=\text{P}^0_\text{A}.$

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