Assertion (A): Henry’s law constant (KH) decreases with increase in temperature.
Reason (R): As the temperature increases, solubility of gases in liquids decreases.
Reason (R): As the temperature increases, solubility of gases in liquids decreases.
Show Hint
- Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
- Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
- Assertion (A) is true, but Reason (R) is false.
- Assertion (A) is false, but Reason (R) is true.
The Correct Option is D
Solution and Explanation
Henry's law states \(p = K_H\, x\), where \(p\) is the partial pressure of the gas, \(x\) is its mole fraction in the solution and \(K_H\) is Henry's law constant.
Step 2: How \(K_H\) relates to solubility.
Rearrange the law to \(x = p / K_H\). At a fixed pressure, a larger \(K_H\) means a smaller mole fraction of dissolved gas, that is, a lower solubility.
Step 3: Check the Reason (R).
Dissolving a gas in a liquid is exothermic. By Le Chatelier's principle, raising the temperature shifts the equilibrium to the side of undissolved gas. Solubility of gases decreases as temperature rises. The Reason is TRUE.
Step 4: Check the Assertion (A).
Since solubility falls with temperature, \(x\) falls at fixed \(p\), so \(K_H = p/x\) must rise. The value of \(K_H\) increases with temperature. The Assertion says it decreases, so it is FALSE.
Step 5: Pick the option.
A is false and R is true. That is option (D). Options (A) and (B) need A to be true, and (C) needs R to be false.
Final Answer:
Assertion is false, Reason is true. The answer is option (D). \[ \boxed{(D)} \]
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