Consider the following data (i) $2 \mathrm{Al}(\mathrm{s})+6 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{Al}_{2} \mathrm{Cl}_{6}(\mathrm{aq})+3 \mathrm{H}_{2}(\mathrm{~g})+ 1200 \mathrm{~kJ} / \mathrm{mol}$. (ii) $\mathrm{H}_{2}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{HCl}(\mathrm{g})+164 \mathrm{~kJ} / \mathrm{mol}$. (iii) $\mathrm{HCl}(\mathrm{g})+\mathrm{aq} \rightarrow \mathrm{HCl}(\mathrm{aq})+83 \mathrm{~kJ} / \mathrm{mol}$. (iv) $\mathrm{Al}_{2} \mathrm{Cl}_{6}(\mathrm{~s})+\mathrm{aq} \rightarrow \mathrm{Al}_{2} \mathrm{Cl}_{6}(\mathrm{aq})+663 \mathrm{~kJ} / \mathrm{mol}$. The enthalpy of formation of anhydrous solid $\mathrm{Al}_{2} \mathrm{Cl}_{6}$ is :

(D) $-1527 \mathrm{~kJ} \mathrm{~mol}^{-1}$

(A) $-648 \mathrm{~kJ} \mathrm{~mol}^{-1}$

(B) $-1350 \mathrm{~kJ} \mathrm{~mol}^{-1}$

(C) $-2002 \mathrm{~kJ} \mathrm{~mol}^{-1}$

JEE Main · 2026 · 02 Apr 2026 · Shift 1 · Chemical Thermodynamics

Consider the following data
(i)

2 Al (s) + 6 HCl (aq) \to Al_{2} Cl_{6} (aq) + 3 H_{2} (g) + 1200 kJ / mol

.
(ii)

H_{2} (g) + Cl_{2} (g) \to 2 HCl (g) + 164 kJ / mol

.
(iii)

HCl (g) + aq \to HCl (aq) + 83 kJ / mol

.
(iv)

Al_{2} Cl_{6} (s) + aq \to Al_{2} Cl_{6} (aq) + 663 kJ / mol

.

The enthalpy of formation of anhydrous solid

Al_{2} Cl_{6}

is :

Answer: (D)

The quantity sought is

Δ_{f} H

for

2 Al (s) + 3 C l_{2} (g) \to A l_{2} C l_{6} (s)

, each listed released heat being an exothermic enthalpy. Add reaction (i),

- 1200

; three times reaction (ii),

3 \times (- 164) = - 492

(which supplies

3 H_{2} + 3 C l_{2} \to 6 HCl (g)

); six times reaction (iii),

6 \times (- 83) = - 498

(dissolving the HCl); and the reverse of reaction (iv),

+ 663

(converting

A l_{2} C l_{6} (a q)

to the solid). The aqueous HCl, hydrogen and

A l_{2} C l_{6} (a q)

terms cancel, leaving

Δ_{f} H = - 1200 - 492 - 498 + 663 = - 1527 kJ mo l^{- 1}

JEE Main · 2026 · 02 Apr 2026 · Shift 1 · Single correct option