Chemical Equilibrium JEE Advanced previous year questions with solutions

3 solved JEE Advanced questions on Chemical Equilibrium, free to read — no sign-in needed. The full chapter has 6 questions; sign in to attempt the remaining 3 in the exam simulator.

1. Q1JEE Advanced Adv 2013 (Paper 2)
   The thermal dissociation equilibrium of ${CaCO}_{3}\left(s⁡\right)$ is studied under different conditions. ${\text{CaCO}}_{3}\left(s⁡\right)\rightleftharpoons \text{CaO}\left(s⁡\right)+{\text{CO}}_{2}\left(\text{g}\right)$ For this equilibrium, the correct statement(s) is/are
   1. A.$∆H$ is dependent on $T.$
   2. B.K is independent of the initial amount of ${\text{CaCO}}_{3}$.
   3. C.$K$ is dependent on the pressure of ${CO}_{2}$​ at a given $T$.
   4. D.$∆H$ is independent of the catalyst, if any.
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   Answer: A,B,D

   Kirchoff's Equation- $\Delta {H}_{T}=\Delta {H}^{^{\circ}}+\int _{298}^{T}{\left(\Delta Cp\right)}_{reac}dT$ $\Delta {\text{H}}_{\text{reac}}$ is dependent on temperature. $\text{K}=\dfrac{\left[{\text{CO}}_{2}\right]\times 1}{1}$ as solids are treated at unit activity. $K$ is independent of initial amount of ${CaCO}_{3}$. ${K}_{p}={pCO}_{2}(g)$ at a given temperature ${K}_{p}$ depends only on temperature. $\Delta \text{H}={\text{E}}_{\text{a}\left(\text{for}\right)}-{\text{E}}_{\text{b}\left(\text{back}\right)}$ A catalyst lowers only the activation energies & $\Delta {\text{H}}_{\text{react}}$ is independent of catalyst.
2. Q2JEE Advanced Adv 2011 (Paper 2)
   The equilibrium $2 \mathrm{Cu}^{\mathrm{I}} \rightleftharpoons \mathrm{Cu}^0+\mathrm{Cu}^{\text {II }}$ in aqueous medium at $25^{\circ} \mathrm{C}$ shifts towards the left in the presence of
   1. A.$\mathrm{NO}_3^{-}$
   2. B.$\mathrm{Cl}^{-}$
   3. C.$\mathrm{SCN}^{-}$
   4. D.$\mathrm{CN}^{-}$
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   Answer: B,C,D

   $\mathrm{Cl}^{-}, \mathrm{CN}^{-}$and $\mathrm{SCN}^{-}$froms precipitate with $\mathrm{Cu}$ (I), remove $\mathrm{Cu}$ (I) ion from equilibrium and reaction shift in direction shift in backward direction according to Le-Chatelier's principle.
3. Q3JEE Advanced Adv 2006
   $\mathrm{Ag}^{+}+\mathrm{NH}_3 \rightleftharpoons\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)\right]^{+} ; k_1=3.5 \times 10^{-3}$ $\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)\right]^{+}+\mathrm{NH}_3 \rightleftharpoons\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right]^{+} ; k_2=1.7 \times 10^{-3}$ then the formation constant of $\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right]^{+}$is
   1. A.$6.08 \times 10^{-6}$
   2. B.$6.08 \times 10^6$
   3. C.$6.08 \times 10^{-9}$
   4. D.None of these
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   Answer: (A)

   (i) $\mathrm{Ag}^{+}+\mathrm{NH}_3 \rightleftharpoons\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)\right]^{+} ; k_1=3.5 \times 10^{-3}$ (ii) $\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)\right]^{+}+\mathrm{NH}_3 \rightleftharpoons\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right]^{+}, k_2=1.7 \times 10^{-3}$ on the basis of above reaction $$\begin{aligned} & k_1=\frac{\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)\right]^{+}}{\left[\mathrm{Ag}^{+}\right]\left[\mathrm{NH}_3\right]} \\ & k_2=\frac{\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right]^{+}}{\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)\right]^{+}\left[\mathrm{NH}_3\right]} \end{aligned}$$ For the formation of $\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right]^{+}$ $$\mathrm{Ag}^{+}+2 \mathrm{NH}_3 \rightleftharpoons\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right]^{+}$$ Formation constant $(K)=\frac{\left[\mathrm{Ag}\left(\mathrm{NH}_3\right)_2\right]^{+}}{\left[\mathrm{Ag}^{+}\right]\left[\mathrm{NH}_3\right]^2}$ From eq. (i) and (ii) $$K=k_1 \times k_2=3.5 \times 10^{-3} \times 1.7 \times 10^{-3}=5.95 \times 10^{-6} \approx 6.08 \times 10^{-6}$$