JEE Main · 2023 · 10 Apr 2023 · Shift 1 · Surface Chemistry

The enthalpy change for the adsorption process and micelle formation respectively are

(A) $Δ H_{ads} < 0$ and $Δ H_{mic} > 0$ ✓ Correct
(B) $Δ H_{ads} < 0$ and $Δ H_{mic} < 0$
(C) $Δ H_{ads} > 0$ and $Δ H_{mic} < 0$
(D) $Δ H_{ads} > 0$ and $Δ H_{mic} > 0$

Answer: (A)

Solution

Adsorption lowers the residual surface forces when gas or solute molecules settle on a surface, and this release of energy makes the process exothermic, so

Δ H_{a d s}

is negative. Micelle formation, on the other hand, is driven mainly by the large gain in entropy when the ordered water around the hydrophobic tails is set free; the accompanying enthalpy change is small and, for most surfactants near room temperature, slightly positive, so

Δ H_{mi c}

is positive. Hence the adsorption enthalpy is negative while the micellisation enthalpy is positive.

JEE Main · 2023 · 10 Apr 2023 · Shift 1 · Single correct option

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JEE Main · 2023 · 10 Apr 2023 · Shift 1 · Surface Chemistry

Solution

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