Consider the given data : (a) $$\begin{aligned} \mathrm{HCl}(\mathrm{~g})+10 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow & \mathrm{HCl} .10 \mathrm{H}_{2} \mathrm{O} \\ & \Delta \mathrm{H}=-69.01 \mathrm{~kJ} \mathrm{~mol}^{-1} \end{aligned}$$ (b) $\mathrm{HCl}(\mathrm{g})+40 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{HCl} .40 \mathrm{H}_{2} \mathrm{O}$ $$\Delta \mathrm{H}=-72.79 \mathrm{~kJ} \mathrm{~mol}^{-1}$$ Choose the correct statement :

(A) Dissolution of gas in water is an endothermic process

(C) The heat of dilution for the $\mathrm{HCl}\left(\mathrm{HCl} \cdot 10 \mathrm{H}_{2} \mathrm{O}\right.$ to $\mathrm{HCl} .40 \mathrm{H}_{2} \mathrm{O}$ ) is $3.78 \mathrm{~kJ} \mathrm{~mol}^{-1}$.

(D) The heat of formation of HCl solution is represented by both (a) and (b)

JEE Main · 2025 · 04 Apr 2025 · Shift 2 · Chemical Thermodynamics

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Consider the given data :
(a)

HCl (g) + 10 H_{2} O (l) \to HCl .10 H_{2} O Δ H = - 69.01 kJ mol^{- 1}

(b)

HCl (g) + 40 H_{2} O (l) \to HCl .40 H_{2} O

Δ H = - 72.79 kJ mol^{- 1}

Choose the correct statement :

(A)Dissolution of gas in water is an endothermic process
(B)The heat of solution depends on the amount of solvent.✓ Correct
(C)The heat of dilution for the $HCl (HCl \cdot 10 H_{2} O$ to $HCl .40 H_{2} O$ ) is $3.78 kJ mol^{- 1}$ .
(D)The heat of formation of HCl solution is represented by both (a) and (b)

Answer: (B)

Solution

Both dissolution enthalpies are negative, so dissolving the gas in water releases heat and is exothermic, not endothermic. Increasing the water from ten to forty moles shifts the enthalpy from

- 69.01

- 72.79 kJ mo l^{- 1}

, so the dilution step itself releases a further

3.78 kJ mo l^{- 1}

and is exothermic, the opposite sign to the value quoted. A heat of formation would require the elements in their standard states, which these processes do not use, so neither equation represents one. What the two different enthalpy values for ten and forty moles of water do show is that the heat of solution depends on the amount of solvent.

JEE Main · 2025 · 04 Apr 2025 · Shift 2 · Single correct option

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JEE Main · 2025 · 04 Apr 2025 · Shift 2 · Chemical Thermodynamics

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