Oxidising power of chlorine in aqueous solution can be determined by the parameters indicated below: $\frac{1}{2} \mathrm{Cl}_{2}(\mathrm{~g}) \xrightarrow{\frac{1}{2} \Delta_{\text {diss }} H^{\ominus}} \mathrm{Cl}(\mathrm{g}) \xrightarrow{\Delta_{\text {eg }} H^{\ominus}} \mathrm{Cl}^{-}(\mathrm{g}) \xrightarrow{\Delta_{\text {hyd }} H^{\ominus}} \mathrm{Cl}^{-}(\mathrm{aq})$. The energy involved in the conversion of $\frac{1}{2} \mathrm{Cl}_{2}(\mathrm{~g})$ to $\mathrm{Cl}^{-}(\mathrm{g})$ (using the data, $\Delta_{\text {diss }} \mathrm{H}_{\mathrm{Cl}_{2}}^{\Theta}=240 \mathrm{kJmol}^{-1}, \Delta_{\mathrm{eg}} \mathrm{H}_{\mathrm{Cl}}^{\Theta}=-349 \mathrm{kJmol}^{-1}, \Delta_{\mathrm{hyd}} \mathrm{H}_{\mathrm{Cl}}^{\Theta}=-381 \mathrm{kJmol}^{-1}$ ) will be

(D) $+120 \mathrm{~kJ} \mathrm{~mol}^{-1}$

JEE Main · 2008 · 27 Apr 2008 · Offline · Chemical Thermodynamics

Oxidising power of chlorine in aqueous solution can be determined by the parameters indicated below:

\frac{1}{2} Cl_{2} (g) \frac{1}{2} Δ_{diss} H^{⊖} Cl (g) Δ_{eg} H^{⊖} Cl^{-} (g) Δ_{hyd} H^{⊖} Cl^{-} (aq)

.
The energy involved in the conversion of

\frac{1}{2} Cl_{2} (g)

Cl^{-} (g)

(using the data,

Δ_{diss} H_{Cl_{2}}^{Θ} = 240 kJmol^{- 1}, Δ_{eg} H_{Cl}^{Θ} = - 349 kJmol^{- 1}, Δ_{hyd} H_{Cl}^{Θ} = - 381 kJmol^{- 1}

)
will be

(A) $+ 152 kJmol^{- 1}$
(B) $- 610 kJmol^{- 1}$ ✓ Correct
(C) $- 850 kJmol^{- 1}$
(D) $+ 120 kJ mol^{- 1}$

Answer: (B)

Solution

The scheme carries half a mole of chlorine gas all the way to hydrated chloride, so three steps contribute: half the dissociation enthalpy to make atomic chlorine, the electron-gain enthalpy to form the gaseous chloride ion, and the hydration enthalpy to take it into solution. Adding them,

\frac{1}{2} (240) + (- 349) + (- 381) = 120 - 349 - 381 = - 610 kJ mo l^{- 1}

. The overall energy change for forming hydrated chloride from half a mole of

C l_{2}

is thus

- 610 kJ mo l^{- 1}

JEE Main · 2008 · 27 Apr 2008 · Offline · Single correct option

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JEE Main · 2008 · 27 Apr 2008 · Offline · Chemical Thermodynamics

Solution

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