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Question #44054

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The Question

The standard Gibbs free energy of dissociation ( $\Delta G^\circ_{diss}$ ) for acetic acid ( $\ce{CH3COOH}$ ) and pivalic acid ( $\ce{(CH3)3CCOOH}$ ) are evaluated at $298\text{ K}$ in two different media: Water ( $\epsilon = 78.4$ ) and the Gas Phase ( $\epsilon = 1$ ). Let $\Delta \Delta G^\circ_{aq} = \Delta G^\circ_{diss, aq}(\text{pivalic}) - \Delta G^\circ_{diss, aq}(\text{acetic})$ and $\Delta \Delta G^\circ_{gas} = \Delta G^\circ_{diss, gas}(\text{pivalic}) - \Delta G^\circ_{diss, gas}(\text{acetic})$ . Which of the following correctly identifies the signs of $\Delta \Delta G^\circ_{aq}$ and $\Delta \Delta G^\circ_{gas}$ , and the dominant physical phenomenon dictating the gas-phase thermodynamic trend?

Options

A.
$\Delta \Delta G^\circ_{aq} > 0$ , $\Delta \Delta G^\circ_{gas} < 0$ , Polarizability effect
B.
$\Delta \Delta G^\circ_{aq} > 0$ , $\Delta \Delta G^\circ_{gas} > 0$ , +I Inductive effect
C.
$\Delta \Delta G^\circ_{aq} < 0$ , $\Delta \Delta G^\circ_{gas} < 0$ , +I Inductive effect
D.
$\Delta \Delta G^\circ_{aq} < 0$ , $\Delta \Delta G^\circ_{gas} > 0$ , Steric hindrance

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Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Standard State Conditions|Carboxylic Acid Strength|Inductive Effect (I-Effect)

Why This Question Is Tricky

Common Mistakes

This question tests a critical 'Chemical Exception' where standard +I inductive effect rules fail.

Students often blindly apply the rule that 'alkyl groups are electron-donating (+I) and destabilize anions' to all environments.

However, the +I effect of alkyl groups is largely an artifact of differential solvation in water.

In the gas phase (or strictly non-polar solvents), polarizability dominates over inductive effects.

Larger alkyl groups actually stabilize anions via charge-induced dipole interactions, completely reversing the expected thermodynamic acidity trend.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Thermodynamics - Class 11 Part 1
Concept	Standard State Conditions
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free