Solution of Chapter 7. Equilibrium (Chemistry - Exemplar Book)

We know that the relationship between K_c and K_p is K_p = K_c (RT)^Δn

What would be the value of ∆n for the reaction

NH₄ Cl (s) ⇋ NH₃ (g) + HCl (g)

For the reaction H₂(g) + I₂(g) ⇋ 2HI (g), the standard free energy is ∆G^⊖ > 0. The Equilibrium constant (K ) would be __________.

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

PCl₅, PCl₃ and Cl₂ are at Equilibrium at 500K 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 K_c for the reaction PCl₅ (g) ⇋ PCl₃ (g) + Cl₂ (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

[Co (H₂O)₆]³⁺ (aq) + 4Cl– (aq) ⇋ [CoCl₄] ^2- (aq) + 6H₂O (l)

(pink) (blue)

The pH of neutral water at 25°C is 7.0. As the temperature increases, ionisation of water increases, however, the concentration of H⁺ ions and OH^– 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 the 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?

K_a1, K_a2 and K_a3 are the respective ionisation constants for the following reactions

H₂ S ⇋ H⁺ + HS^-

HS ⇋ H⁺ + S^2-

H₂S ⇋ 2H⁺ + S^2-

The correct relationship between K_a1 , K_a2 and K_a3 is

The acidity of BF₃ 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 CH₃COOH (K_a = 1.74 × 10^-5 )?

K_a for CH3COOH is 1.8 × 10^-5 and Kb for NH₄OH is 1.8 × 10^-5. The 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 Le Chatelier’s principle. Consider the reaction.

N₂ (g) + 3H₂ (g) ⇋ 2NH₃ (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 a maximum boiling point and ether has a minimum boiling point?

At 500 K, Equilibrium constant, K_c, for the following reaction is 5.

1/2 H₂(g) + 1/2 I₂ (g) ⇋ HI (g)

What would be the Equilibrium constant K_c for the reaction

2HI (g) ⇋ H₂(g) + I₂ (g)

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

For the reaction N₂O₄ (g) ⇋ 2NO₂ (g), the value of K is 50 at 400 K and 1700 at 500 K. Which of the following options is correct?

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?

The ionization of hydrochloric in water is given below:

HCl (aq) + H₂O (l) ⇋ H₃ O⁺ (aq) + Cl^- (aq)

Label two conjugate acid-base pairs in this ionization.

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 ionization and how is it affected by the concentration of sodium chloride?

BF₃ does not have proton but still acts as an acid and reacts with NH₃. Why is it so? What type of bond is formed between the two?

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

K_b =

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

Base Di-methylamine Urea Pyridine Ammonia

K_b 5.4 × 10_-4 1.3 × 10^-14 1.77× 10^-9 1.77 × 10^-5

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

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

OH^-, RO^-, CH₃COO^-, Cl^-

Arrange the following in increasing order of pH

KNO₃ (aq), CH₃COONa (aq), NH₄Cl (aq), C₆ H₅COONH₄ (aq)

The value of K_c for the reaction 2HI (g) ⇋ H₂ (g) + I₂ (g) is 1 × 10^-4

At a given time, the composition of the reaction mixture is

[HI] =2 × 10^-5 mol, [H₂] =1 × 10^-5 mol and [I₂] =1 × 10^-5 mol. In which direction will the reaction proceed?

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

The pH of a solution of a strong acid is 5.0. What will be the pH of the solution obtained after diluting the given solution a 100 times?

A sparingly soluble salt gets precipitated only when the product of the concentration of its ions in the solution (Q_sp) becomes greater than its solubility product. If the solubility of BaSO₄ in water is 8 × 10^-4 mol dm^-3, calculate its solubility in 0.01 mol dm^-3 of H₂SO₄.

pH of 0.08 mol dm^-3 HOCl solution is 2.85. Calculate its ionisation constant.

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

The solubility product of Al(OH) ₃ is 2.7 × 10^-11. Calculate its solubility in gL^-1 and also find out the pH of this solution. (Atomic mass of Al = 27 u).

Calculate the volume of water required to dissolve 0.1 g lead (II) chloride to get a saturated solution. (K_sp of PbCl₂ = 3.2 × 10^-8, atomic mass of Pb = 207 u).

A reaction between ammonia and boron trifluoride is given below:

: NH₃ + BF₃→ H₃N: BF₃

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: CaCO₃ (s) → CaO₃ (s) + CO₂ (g)

Δ_fH^⊖ [CaO (s)] = -635.1 kJ mol^=-1

Δ_fH^⊖ [CO₂ (g)] = -393.5 kJ mol^-1

Δ_fH^⊖ [CaCO₃ (s)] = -1206.9 kJ mol^-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: N₂ (g) + 3H₂ (g) ⇋ 2NH₃ (g)

Equilibrium constant K_c =

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

Column I (Reaction) Column II (Equilibrium constant)

Match standard free energy of the reaction with the corresponding Equilibrium constant

Match the following species with the corresponding conjugate acid

Species 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)

Column I Column II

(i) Equilibrium (a) ∆G > 0, K < 1

(ii) Spontaneous reaction (b) ∆G = 0

(iii) Non spontaneous reaction (c) ∆G^⊖ = 0

(d) ∆G < 0, K >1

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): Increasing order of acidity of hydrogen halides is HF < HCl < HBr < HI

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

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A) : A solution containing a mixture of acetic acid and sodium acetate maintains a constant value of 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 pH 4.75.

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

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.

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

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.

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

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 Ka and Kb value of the acid and the base forming it.

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

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

Reason (R) : Acetic acid is a weak acid and NH4OH is a weak base.

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): In the dissociation of PCl5 at constant pressure and temperature addition of helium at Equilibrium increases the dissociation of PCl₅ .

Reason (R) : Helium removes Cl₂ 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.

N₂ (g) + 3H₂ (g) ⇋ 2NH₃ (g) Δ H = -92.38 kJ mil^-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 A^p+_x B^q-_y 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 of each term and answer the following :

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

(b) Explain the effect of increase in pressure in terms of reaction quotient Q. for the reaction: CO(g) + 3H₂(g) + 3H₂ (g) ⇋ CH₄ (g) + H₂ O (g)