NCERT Exemplar solutions for Chemistry [English] Class 11 chapter 7 - Equilibrium [Latest edition]

We know that the relationship between K_c and K_p is K_p = K_c (RT)^∆n What would be the value of ∆n for the reaction $$\mathrm{NH}{\phantom{A}}_4\mathrm{Cl}(\mathrm{s})\stackrel{-\rightharpoonup }{\leftharpoondown -}\mathrm{NH}{\phantom{A}}_3(\mathrm{g})+\mathrm{HCl}(\mathrm{g})$$

For the reaction $$\mathrm{H}{\phantom{A}}_2(\mathrm{g})+\mathrm{I}{\phantom{A}}_2(\mathrm{g})\stackrel{-\rightharpoonup }{\leftharpoondown -}2\mathrm{HI}(\mathrm{g})$$, the standard free energy is  ∆G^Θ > 0. The equilibrium constant (K ) would be ______.

Which of the following is not a general characteristic of equilibria involving physical processes?

$$\mathrm{PCl}{\phantom{A}}_5,\mathrm{PCl}{\phantom{A}}_3\mathrm{and}\mathrm{Cl}{\phantom{A}}_2$$ are at equilibrium at 500 K in a closed container and their concentrations are 0.8 × 10^–3 mol L^–1, 1.2 × 10^–3 mol L^–1 and 1.2 × 10^–3 mol L^–1 respectively. The value of Kc for the reaction $$\mathrm{PCl}{\phantom{A}}_5(\mathrm{g})\stackrel{-\rightharpoonup }{\leftharpoondown -}\mathrm{PCl}{\phantom{A}}_3(\mathrm{g})+\mathrm{Cl}{\phantom{A}}_2(\mathrm{g})$$ will be ______.

Which of the following statements is incorrect?

When hydrochloric acid is added to cobalt nitrate solution at room temperature, the following reaction takes place and the reaction mixture becomes blue. On cooling the mixture it becomes pink. On the basis of this information mark the correct answer.

$$\underset{(\mathrm{pink})}{[\mathrm{Co}(\mathrm{H}{\phantom{A}}_2\mathrm{O}){\phantom{A}}_6]{\phantom{A}}^{3+}}(\mathrm{aq})+4\mathrm{Cl}{\phantom{A}}^{-}(\mathrm{qa})\stackrel{-\rightharpoonup }{\leftharpoondown -}\underset{(\mathrm{blue})}{[\mathrm{CoCl}{\phantom{A}}_4]{\phantom{A}}^{2-}}(\mathrm{aq})+6\mathrm{H}{\phantom{A}}_2\mathrm{O}(\mathrm{l})$$

The pH of neutral water at 25°C is 7.0. As the temperature increases, ionisation of water increases, however, the concentration of $$\mathrm{H}{\phantom{A}}^{+}$$ ions and $$\mathrm{OH}{\phantom{A}}^{-}$$ ions are equal. What will be the pH of pure water at 60°C?

The ionisation constant of an acid, K_a, is the measure of strength of an acid. The K_a values of acetic acid, hypochlorous acid and formic acid are 1.74 × 10^–5, 3.0 × 10^–8 and 1.8 × 10^–4 respectively. Which of the following orders of pH of 0.1 mol dm^–3 solutions of these acids is correct?

$$\mathrm{K}{\phantom{A}}_{{\mathrm{a}}_1},\mathrm{K}{\phantom{A}}_{{\mathrm{a}}_2}$$ and $$\mathrm{K}{\phantom{A}}_{{\mathrm{a}}_3}$$ are the respective ionisation constants for the following reactions.

$$\mathrm{H}{\phantom{A}}_2\mathrm{S}\stackrel{-\rightharpoonup }{\leftharpoondown -}\mathrm{H}{\phantom{A}}^{+}+\mathrm{Hs}{\phantom{A}}^{-}$$

$$\mathrm{Hs}{\phantom{A}}^{-}\stackrel{-\rightharpoonup }{\leftharpoondown -}\mathrm{H}{\phantom{A}}^{+}+\mathrm{S}{\phantom{A}}^{2-}$$

$$\mathrm{H}{\phantom{A}}_2\mathrm{S}\stackrel{-\rightharpoonup }{\leftharpoondown -}2\mathrm{H}{\phantom{A}}^{+}+\mathrm{S}{\phantom{A}}^{2-}$$

The correct relationship between $$\mathrm{K}{\phantom{A}}_{{\mathrm{a}}_1},\mathrm{K}{\phantom{A}}_{{\mathrm{a}}_2}$$ and $$\mathrm{K}{\phantom{A}}_{{\mathrm{a}}_3}$$ is ______.

Acidity of $$\mathrm{BF}{\phantom{A}}_3$$ can be explained on the basis of which of the following concepts?

Which of the following will produce a buffer solution when mixed in equal volumes?

In which of the following solvents is silver chloride most soluble?

What will be the value of pH of 0.01 mol dm^–3 $$\mathrm{CH}{\phantom{A}}_3\mathrm{COOH}$$ (K_a = 1.74 × 10^–5)?

$$\mathrm{K}{\phantom{A}}_a$$ for $$\mathrm{CH}{\phantom{A}}_3\mathrm{COOH}$$ is 1.8 × 10^–5 and $$\mathrm{K}{\phantom{A}}_b$$ for $$\mathrm{NH}{\phantom{A}}_4\mathrm{OH}$$ is 1.8 × 10^–5 . The $$\mathrm{pH}$$ of ammonium acetate will be ______.

Which of the following options will be correct for the stage of half completion of the reaction A ⇌ B.

On increasing the pressure, in which direction will the gas phase reaction proceed to re-establish equilibrium, is predicted by applying the Le Chatelier’s principle. Consider the reaction.

$$\mathrm{N}{\phantom{A}}_2(\mathrm{g})+3\mathrm{H}{\phantom{A}}_2(\mathrm{g})\stackrel{-\rightharpoonup }{\leftharpoondown -}2\mathrm{NH}{\phantom{A}}_3(\mathrm{g})$$

Which of the following is correct, if the total pressure at which the equilibrium is established, is increased without changing the temperature?

What will be the correct order of vapour pressure of water, acetone and ether at 30°C. Given that among these compounds, water has maximum boiling point and ether has minimum boiling point?

At 500 K, equilibrium constant, $$\mathrm{K}{\phantom{A}}_c$$, for the following reaction is 5.

$$\frac{1}{2}\mathrm{H}{\phantom{A}}_2(\mathrm{g})+\frac{1}{2}\mathrm{I}{\phantom{A}}_2(\mathrm{g})\stackrel{-\rightharpoonup }{\leftharpoondown -}\mathrm{HI}(\mathrm{g})$$

What would be the equilibrium constant $$\mathrm{K}{\phantom{A}}_c$$ for the reaction

$$2\mathrm{HI}(\mathrm{g})\stackrel{-\rightharpoonup }{\leftharpoondown -}\mathrm{H}{\phantom{A}}_2(\mathrm{g})+\mathrm{I}{\phantom{A}}_2(\mathrm{g})$$

In which of the following reactions, the equilibrium remains unaffected on addition of small amount of argon at constant volume?

For the reaction $$\mathrm{N}{\phantom{A}}_2\mathrm{O}{\phantom{A}}_4(\mathrm{g})\stackrel{-\rightharpoonup }{\leftharpoondown -}2\mathrm{NO}{\phantom{A}}_2(\mathrm{g})$$, the value of K is 50 at 400 K and 1700 at 500 K. Which of the following options is correct?

(i) The reaction is endothermic.

(ii) The reaction is exothermic.

T

(iv) The entropy of the system increases.

At a particular temperature and atmospheric pressure, the solid and liquid phases of a pure substance can exist in equilibrium. Which of the following term defines this temperature?

(i) Normal melting point

(ii) Equilibrium temperature

(iii) Boiling point

(iv) Freezing point

The ionisation of hydrochloric in water is given below:

$$\mathrm{HCl}(\mathrm{aq})+\mathrm{H}{\phantom{A}}_2\mathrm{O}(\mathrm{l})\stackrel{-\rightharpoonup }{\leftharpoondown -}\mathrm{H}{\phantom{A}}_3\mathrm{O}{\phantom{A}}^{+}(\mathrm{aq})+\mathrm{Cl}{\phantom{A}}^{-}(\mathrm{aq})$$

Label two conjugate acid-base pairs in this ionisation.

The aqueous solution of sugar does not conduct electricity. However, when sodium chloride is added to water, it conducts electricity. How will you explain this statement on the basis of ionisation and how is it affected by concentration of sodium chloride?

$$\mathrm{BF}{\phantom{A}}_3$$ does not have proton but still acts as an acid and reacts with $$\mathrm{NH}{\phantom{A}}_3$$. Why is it so? What type of bond is formed between the two?

Ionisation constant of a weak base MOH, is given by the expression

${\displaystyle K_b=\frac{\left[M^{+}\right]\left[O{H}^{-}\right]}{\left[MOH\right]}}$

Values of ionisation constant of some weak bases at a particular temperature are given below:

Arrange the bases in decreasing order of the extent of their ionisation at equilibrium. Which of the above base is the strongest?

Conjugate acid of a weak base is always stronger. What will be the decreasing order of basic strength of the following conjugate bases?

$$\mathrm{OH}{\phantom{A}}^{-},\mathrm{RO}{\phantom{A}}^{-},\mathrm{CH}{\phantom{A}}_3\mathrm{COO}{\phantom{A}}^{-},\mathrm{Cl}{\phantom{A}}^{-}$$

Arrange the following in increasing order of $$\mathrm{pH}$$.

$$\mathrm{KNO}{\phantom{A}}_3(\mathrm{aq}),\mathrm{CH}{\phantom{A}}_3\mathrm{COONa}(\mathrm{aq}),\mathrm{NH}{\phantom{A}}_4\mathrm{Cl}(\mathrm{aq}),\mathrm{C}{\phantom{A}}_6\mathrm{H}{\phantom{A}}_5\mathrm{COONH}{\phantom{A}}_4(\mathrm{aq})$$

The value of $$\mathrm{K}{\phantom{A}}_c$$ for the reaction $$2\mathrm{HI}(\mathrm{g})\stackrel{-\rightharpoonup }{\leftharpoondown -}\mathrm{H}{\phantom{A}}_2(\mathrm{g})+\mathrm{I}{\phantom{A}}_2(\mathrm{g})$$ is 1 × 10^–4 At a given time, the composition of reaction mixture is $$[\mathrm{HI}]$$ = 2 × 10^–5 mol, $$[\mathrm{HI}]$$ = 1 × 10^–5 mol and $$[\mathrm{I}{\phantom{A}}_2]$$ = 1 × 10^–5 mol In which direction will the reaction proceed?

On the basis of the equation $$\mathrm{pH}$$ = – log $$[\mathrm{H}{\phantom{A}}^{+}]$$, the $$\mathrm{pH}$$ of 10^–8 mol dm^–3 solution of $$\mathrm{HCl}$$ should be 8. However, it is observed to be less than 7.0. Explain the reason.

$$\mathrm{pH}$$ of a solution of a strong acid is 5.0. What will be the $$\mathrm{pH}$$ of the solution obtained after diluting the given solution a 100 times?

A sparingly soluble salt gets precipitated only when the product of concentration of its ions in the solution (Q_sp) becomes greater than its solubility product. If the solubility of $$\mathrm{BaSO}{\phantom{A}}_4$$ in water is 8 × 10^–4 mol dm^–3. Calculate its solubility in 0.01 mol dm^–3 of $$\mathrm{H}{\phantom{A}}_2\mathrm{SO}{\phantom{A}}_4$$.

$$\mathrm{pH}$$ of 0.08 mol dm^–3 $$\mathrm{HOCl}$$ solution is 2.85. Calculate its ionisation constant

Calculate the $$\mathrm{pH}$$ of a solution formed by mixing equal volumes of two solutions A and B of a strong acid having $$\mathrm{pH}$$ = 6 and $$\mathrm{pH}$$ = 4 respectively.

The solubility product of $$\mathrm{Al}(\mathrm{OH}){\phantom{A}}_3$$ is 2.7 × 10^–11. Calculate its solubility in gL^–1 and also find out pH of this solution. (Atomic mass of $$\mathrm{Al}=27\mathrm{u}$$).

Calculate the volume of water required to dissolve 0.1 g lead (II) chloride to get a saturated solution. $$(\mathrm{K}{\phantom{A}}_{\mathrm{sp}}\mathrm{of}\mathrm{PbCl}{\phantom{A}}_2$$ = 3.2 × 10^–8, atomic mass of $$\mathrm{Pb}=207\mathrm{u}$$).

A reaction between ammonia and boron trifluoride is given below: $$\mathrm{NH}{\phantom{A}}_3+\mathrm{BF}{\phantom{A}}_3⟶\mathrm{H}{\phantom{A}}_3\mathrm{N}:\mathrm{BF}{\phantom{A}}_3$$ Identify the acid and base in this reaction. Which theory explains it? What is the hybridisation of B and N in the reactants?

Following data is given for the reaction: $$\mathrm{CaCO}{\phantom{A}}_3(\mathrm{S})⟶\mathrm{CaO}(\mathrm{s})+\mathrm{CO}{\phantom{A}}_2(\mathrm{g})$$

$$∆{\phantom{A}}_f\mathrm{H}{\phantom{A}}^{\mathrm{\Theta }}[\mathrm{CaO}(\mathrm{s})]=-635.1\mathrm{kJ}\mathrm{mo}{\phantom{A}}^{-1}$$

$$∆{\phantom{A}}_f\mathrm{H}{\phantom{A}}^{\mathrm{\Theta }}[\mathrm{CO}{\phantom{A}}_2(\mathrm{g})]=-393.5\mathrm{kJ}\mathrm{mol}{\phantom{A}}^{-1}$$

$$∆{\phantom{A}}_f\mathrm{H}{\phantom{A}}^{\mathrm{\Theta }}[\mathrm{CaCO}{\phantom{A}}_3(\mathrm{s})]=-1206.9\mathrm{kJ}\mathrm{mol}{\phantom{A}}^{-1}$$

Predict the effect of temperature on the equilibrium constant of the above reaction.

Match the following equilibria with the corresponding condition:

For the reaction : $$\mathrm{N}{\phantom{A}}_2(\mathrm{g})+3\mathrm{H}{\phantom{A}}_2(\mathrm{g})\stackrel{-\rightharpoonup }{\leftharpoondown -}2\mathrm{NH}{\phantom{A}}_3(\mathrm{g})$$

Equilibrium constant ${\displaystyle K_C=\frac{{\left[NH3\right]}^2}{\left[N_2\right]{\left[H_2\right]}^3}}$

Some reactions are written below in Column I and their equilibrium constants in terms of Kc are written in Column II. Match the following reactions with the corresponding equilibrium constant

Match standard free energy of the reaction with the corresponding equilibrium constant.

Match the following species with the corresponding conjugate acid:

Match the following graphical variation with their description

A	B
(i)	(a) Variation in product concentration with time
(ii)	(b) Reaction at equilibrium
(iii)	(c) Variation in reactant concentration with time

Match Column (I) with Column (II).

Assertion (A): Increasing order of acidity of hydrogen halides is $$\mathrm{HF}<\mathrm{HCl}<\mathrm{HBr}<\mathrm{HI}$$

Reason (R): While comparing acids formed by the elements belonging to the same group of periodic table, $$\mathrm{H}-\mathrm{A}$$ bond strength is a more important factor in determining acidity of an acid than the polar nature of the bond.

Assertion (A): A solution containing a mixture of acetic acid and sodium acetate maintains a constant value of $$\mathrm{pH}$$ on addition of small amounts of acid or alkali.

Reason (R): A solution containing a mixture of acetic acid and sodium acetate acts as a buffer solution around $$\mathrm{pH}$$ 4.75.

Assertion (A): The ionisation of hydrogen sulphide in water is low in the presence of hydrochloric acid.

Reason (R): Hydrogen sulphide is a weak acid.

Assertion (A): For any chemical reaction at a particular temperature, the equilibrium constant is fixed and is a characteristic property.

Reason (R): Equilibrium constant is independent of temperature.

Assertion (A): Aqueous solution of ammonium carbonate is basic.

Reason (R): Acidic/basic nature of a salt solution of a salt of weak acid and weak base depends on K_a and K_b value of the acid and the base forming it.

Assertion (A): An aqueous solution of ammonium acetate can act as a buffer.

Reason (R): Acetic acid is a weak acid and $$\mathrm{NH}{\phantom{A}}_4\mathrm{OH}$$ is a weak base.

Assertion (A): In the dissociation of $$\mathrm{PCl}{\phantom{A}}_5$$ at constant pressure and temperature addition of helium at equilibrium increases the dissociation of $$\mathrm{PCl}{\phantom{A}}_5$$.

Reason (R): Helium removes $$\mathrm{Cl}{\phantom{A}}_2$$ from the field of action.

How can you predict the following stages of a reaction by comparing the value of K_c and Q_c?

(i) Net reaction proceeds in the forward direction.

(ii) Net reaction proceeds in the backward direction.

(iii) No net reaction occurs.

On the basis of Le Chatelier principle explain how temperature and pressure can be adjusted to increase the yield of ammonia in the following reaction.

$$\mathrm{N}{\phantom{A}}_2(\mathrm{g})+3\mathrm{H}{\phantom{A}}_2(\mathrm{g})\stackrel{-\rightharpoonup }{\leftharpoondown -}2\mathrm{NH}{\phantom{A}}_3(\mathrm{g})∆\mathrm{H}=-92.38\mathrm{kJ}\mathrm{mol}{\phantom{A}}^{-1}$$

What will be the effect of addition of argon to the above reaction mixture at constant volume?

A sparingly soluble salt having general formula $$\mathrm{A}{\phantom{A}}_x^{p+}\mathrm{B}{\phantom{A}}_y^{q-}$$ and molar solubility S is in equilibrium with its saturated solution. Derive a relationship between the solubility and solubility product for such salt.

Write a relation between ∆G and Q and define the meaning term and answer the following:

Why a reaction proceeds forward when Q < K and no net reaction occurs when Q = K.

Write a relation between ∆G and Q and define the meaning term and answer the following:

Explain the effect of increase in pressure in terms of reaction quotient Q. for the reaction: $$\mathrm{CO}(\mathrm{g})+3\mathrm{H}{\phantom{A}}_2(\mathrm{g})\stackrel{-\rightharpoonup }{\leftharpoondown -}\mathrm{CH}{\phantom{A}}_4(\mathrm{g})+\mathrm{H}{\phantom{A}}_2\mathrm{O}(\mathrm{g})$$