Chapter 7 - Equilibrium

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.
(i) Both A and R are true and R is correct explanation of A.
(ii) Both A and R are true but R is not correct explanation of A.
(iii) A is false but R is true.
(iv) Both A and R are false.

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.
(i) Both A and R are true and R is correct explanation of A.
(ii) Both A and R are true but R is not correct explanation of A.
(iii) A is true but R is false.
(iv) Both A and R are false.

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.
(i) Both A and R are true and R is correct explanation of A.
(ii) Both A and R are true but R is not correct explanation of A.
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95 Equilibrium
(iii) A is true but R is false
(iv) Both A and R are false

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.

(i) Both A and R are true and R is correct explanation of A.
(ii) Both A and R are true but R is not the correct explanation of A.
(iii) A is true but R is false.
(iv) Both A and R are false.

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.
(i) Both A and R are true and R is the correct explanation of A.
(ii) Both A and R are true but R is not the correct explanation of A.
(iii) A is true but R is false.
(iv) Both A and R are false.

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.

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?

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?

Name a basic buffer having pH around 10.

Calculate the solubility of Ag Cl (s) in pure water.

Calculate the pH of a buffer solution containing 0.1 mole of acetic acid and
0.15 mole of sodium acetate. Ionisation constant for acetic acid is 1.75 × 10^-5.

How does dilution with water affect the pH of a buffer solution?

Ksp for Hg SO4 is 6.4 x 10^-5. What is the solubility of the salt?

Give an example of acidic buffer?

When is a solution called unsaturated?

Define solubility product.

Define Buffer solution.

The concentration of H+ in a soft drink is 3.8 x 10^-3 M. what is its p^H?

Calculate the pH of the solution

0.002 MHBr

Show that, in aqueous solutions

p^H + p^OH = p^kw

What is the value of p^H + p^OH at 250c?

A solution give the following colors with different indicators. Methyl orange –

yellow, methyl red – yellow, and bromothymol blue Orange . what is the pH of

the solution?

The pka of acetic acid and pkb of ammonium hydroxide are 4.76 and 4.75

respectively. Calculate the pH of ammonium acetate solution

The degree of dissociation of N₂O₄,

N₂O₄(g) ⇌2NO2(g), at temperature T and total pressure is α. Find the

expression for the equilibrium constant of this reaction at this temperature

and pressure?

What is the concentration of H₃O⁺ and OH^- ions in water at 298K?

What happens to the pH if a few drops of acid are added to CH3COONH₄

solution?

If pH of a solution is 7, calculate its pOH value

The dimethyl ammonium ion, (CH₃)₂ NH₂

+, is a weak acid and ionizes to a

slight degree in water what is its conjugate base?

Justify the statement that water behaves like an acid and also like a base on
the basis of protonic concept.

Predict if the solutions of the following salts are neutral, acidic or basic :

NaCl, KBr, NaCN, NaOH H₂SO₄, NaNO₂, NH₄ NO₃, KF

Select Lewis acid and Lewis base from the following :

Cu²⁺ , H₂O, BF₃ OH-

What is the difference between a conjugate acid and a conjugate base?

Give two examples of actions which can act as hour’s acids

Which conjugate base is stronger CN- or F- ?

Write the conjugate acids for the following Bronsted bases : NH2, NH3 and
HCOO-.

Define strong and weak electrolyte.

(i) In the reaction equilibrium
A + B ⇌C +D,
What will happen to the concentrations of A, B and D if concentration of C is
increased.
(ii) what will happen if concentration of A is increased?

Using Le – chatelier principle, predict the effect of

(a) decreasing the temperature

(b) increasing the temperature

in each of the following equilibrium systems:

(i) N₂ (g) + 3H₂(g) ⇌2NH₃(g) + D

(ii) N₂(g) + O₂(g) + D⇌2NO(g)

If Qc < Kc, when we continuously remove the product, what would be the
direction of the reaction?

Can a catalyst change the position of equilibrium in a reaction?

The equilibrium constant of a reaction increases with rise in temperature. Is
the reaction exo – or endothermic?

What happens when temperature increases for a reaction?

What is the effect of reducing the volume on the system described below?

2C(s) + O₂(g) ⇌2CO(g)

Can a catalyst change the position of equilibrium in a reaction?

State Le chatelier’s principle.

On what factors does the value of the equilibrium constant of a reaction
depend?

The dissociation of HI is independent of pressure, while dissociation of PCl₅

depends upon the pressure applied. Why?

Write the equilibrium constant expression for each of the following reactions.

In each case, indicate which of the reaction is homogeneous or heterogeneous.

(a) 2CO(g) +O₂(g) ⇌2CO2(g)

(b) N₂O₅(g) ⇌ NO2 (g) + NO₃(g)

(c) Zn(s) + 2HCl (g) ⇌ZnCl₂(s) +H₂(g)

(d) 2H₂O(l) ⇌2H₂O (l) + O₂(g)

The value of Kc for the reaction

2A ⇌B+C is 2x10^-3. At a given time, the composition of the reaction mixture

is [A] = [B] =[C] = 3x10^-4 M. In which direction the reaction will proceed?

What inference you get when Qc = Kc?

If Qc > Kc, what would be the type of reaction?

Define reaction quotient.

Give the generalizations concerning the composition of equilibrium mixtures.

The equilibrium constant for the reaction H₂O + CO ⇌H₂ + CO₂

Is 0.44 at 1260k. What will be the value of the equilibrium constant for the

reaction : 2H₂ (g) + 2CO (g) ⇌2CO(g) + 2H₂O (g) at 1260 K

Write the expression for equilibrium constant Kp for the reaction

3Fe (s) + 4H₂O ⇌Fe₃O₄ (s) + 4H₂(g)

Write the relationship between Kp and Kc for the following reactions:

(a) PCl₅ ⇌PCl₃ (q)+ Cl₂(q)

(b) N₂ (q)+ 3H₂ (q)⇌2NH₃(g)

(c) H₂(g) + I₂(g)⇌2HI(g)

(d) 2H₂O(g) ⇌2H₂O (g) +O₂(g)

Give the relation Kp = Kc (RT)Dn .

What is the unit of equilibrium for the reaction N₂(g) + 3H₂(g) ⇌2NH₃ (g).

When the total number of moles of product and reactants are equal, K has no
unit. Give reason.

Write the expression for the equilibrium constant for the reaction :

4NH₃ (g) + 502 (g) ⇌4NO (g) + 6H₂ O (g)

Write the equilibrium constant for the following equation :
aA +bB ⇌cC + dD

Write the equilibrium constant for the following equation :
aA +bB ⇌cC + dD

State the law of chemical equilibrium.

What conclusion is drawn from the following –

Solid ⇌Liquid

H₂O(s) ⇌ H₂O 

Mention the general characteristics of equilibria involving physical processes

On which factor does the concentration of solute in a saturated solution
depends?

What happens to the boiling point of water at high altitude?

State Henry’s law.

On what factor does the boiling point of the liquid depends?

What is meant by the statement ‘Equilibrium is dynamic in nature’?

What is physical equilibrium? Give an example.

Name the three group into which chemical equilibrium can be classified

Define dynamic equilibrium.

The concentration of sulphide ion in 0.1M HCl solution saturated with hydrogen sulphide is 1.0 × 10^–19 M. If 10 mL of this is added to 5 mL of 0.04 M solution of the following: FeSO₄, MnCl₂, ZnCl₂ and CdCl₂. in which of these solutions precipitation will take place?

What is the minimum volume of water required to dissolve 1g of calcium sulphate at 298 K? (For calcium sulphate, K_sp is 9.1 x 10^-6).

What is the maximum concentration of equimolar solutions of ferrous sulphate and sodium sulphide so that when mixed in equal volumes, there is no precipitation of iron sulphide? (For iron sulphide, K_sp = 6.3 x 10^-18).

The ionization constant of benzoic acid is 6.46 x 10^-5 and K_sp for silver benzoate is 2.5 x 10^-13. How many times is silver benzoate more soluble in a buffer of pH 3.19 compared to its solubility in pure water?

Equal volumes of 0.002 M solutions of sodium iodate and cupric chlorate are mixed together. Will it lead to precipitation of copper iodate? (For cupric iodate K_sp = 7.4 x 10^-8).

The solubility product constant of Ag₂CrO₄ and AgBr are 1.1 x 10^-12 and 5.0 x 10^-13 respectively. Calculate the ratio of the molarities of their saturated solutions.

Determine the solubilities of silver chromate, barium chromate, ferric hydroxide, lead chloride and mercurous iodide at 298K from their solubility product constants given in Table 7.9 (page 221). Determine also the molarities of individual ions.

Calculate the pH of the resultant mixtures:

a) 10 mL of 0.2M Ca(OH)₂ + 25 mL of 0.1M HCl

b) 10 mL of 0.01M H₂SO₄ + 10 mL of 0.01M Ca(OH)₂

c) 10 mL of 0.1M H₂SO₄ + 10 mL of 0.1M KOH

The ionization constant of chloroacetic acid is 1.35 x 10^-3. What will be the pH of 0.1M acid and its 0.1M sodium salt solution?

Predict if the solutions of the following salts are neutral, acidic or basic:

NaCl, KBr, NaCN, NH4NO3, NaNO2 and KF

A 0.02 M solution of pyridinium hydrochloride has pH = 3.44. Calculate the ionization constant of pyridine

The ionization constant of nitrous acid is 4.5 x 10^-4. Calculate the pH of 0.04 M sodium nitrite solution and also its degree of hydrolysis.

The pH of 0.1M solution of cyanic acid (HCNO) is 2.34. Calculate the ionization constant of the acid and its degree of ionization in the solution.

The ionization constant of propanoic acid is 1.32 x 10^-5. Calculate the degree of ionization of the acid in its 0.05M solution and also its pH. What will be its degree of ionization if the solution is 0.01M in HCl also?

The solubility of Sr(OH)₂ at 298 K is 19.23 g/L of solution. Calculate the concentrations of strontium and hydroxyl ions and the pH of the solution.

If 0.561 g of KOH is dissolved in water to give 200 mL of solution at 298 K. Calculate the concentrations of potassium, hydrogen and hydroxyl ions. What is its pH?

The pH of milk, black coffee, tomato juice, lemon juice and egg white are 6.8, 5.0, 4.2, 2.2 and 7.8 respectively. Calculate corresponding hydrogen ion concentration in each.

Calculate the hydrogen ion concentration in the following biological fluids whose pH are given below:

(a) Human muscle-fluid, 6.83

(b) Human stomach fluid, 1.2

(c) Human blood, 7.38

(d) Human saliva, 6.4.

The ionization constant of dimethylamine is 5.4 x 10^-4. Calculate its degree of ionization in its 0.02 M solution. What percentage of dimethylamine is ionized if the solution is also 0.1 M in NaOH?

Calculate the degree of ionization of 0.05M acetic acid if its pK_a value is 4.74.

How is the degree of dissociation affected when its solution also contains (a) 0.01 M (b) 0.1 M in HCl?

What is the pH of 0.001 M aniline solution? The ionization constant of aniline can be taken from Table 7.7. Calculate the degree of ionization of aniline in the solution. Also calculate the ionization constant of the conjugate acid of aniline.

The pH of 0.005M codeine (C₁₈H₂₁NO₃) solution is 9.95. Calculate its ionization constant and pK_b.

The degree of ionization of a 0.1M bromoacetic acid solution is 0.132. Calculate the pH of the solution and the pK_a of bromoacetic acid.

Calculate the pH of the following solutions:

a) 2 g of TlOH dissolved in water to give 2 litre of solution.

b) 0.3 g of Ca(OH)2 dissolved in water to give 500 mL of solution.

c) 0.3 g of NaOH dissolved in water to give 200 mL of solution.

d) 1mL of 13.6 M HCl is diluted with water to give 1 litre of solution.

Assuming complete dissociation, calculate the pH of the following solutions:

(a) 0.003 M HCl      (b) 0.005 M NaOH      (c) 0.002 M HBr      (d) 0.002 M KOH

It has been found that the pH of a 0.01M solution of an organic acid is 4.15. Calculate the concentration of the anion, the ionization constant of the acid and its pK_a.

The ionization constant of acetic acid is 1.74 x 10-5. Calculate the degree of dissociation of acetic acid in its 0.05 M solution. Calculate the concentration of acetate ion in the solution and its pH.

The species: H₂O, , and NH₃ can act both as Brönsted acids and bases. For each case give the corresponding conjugate acid and base.

will be the conjugate bases for the Brönsted acids: HF, H₂SO₄ and HCO₃?

What will be the conjugate bases for the Brönsted acids: HF, H₂SO₄ and HCO₃?

Which of the followings are Lewis acids? H₂O, BF₃, H⁺, and 

What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species:

The reaction, CO(g) + 3H₂(g)CH₄(g) + H₂O(g) is at equilibrium at 1300 K in a 1L flask. It also contain 0.30 mol of CO, 0.10 mol of H₂ and 0.02 mol of H₂O and an unknown amount of CH₄ in the flask. Determine the concentration of CH₄ in the mixture. The equilibrium constant, K_c for the reaction at the given temperature is 3.90.

The value of K_c for the reaction

3O₂ (g)  2O₃ (g)

is 2.0 ×10^–50 at 25°C. If the equilibrium concentration of O₂ in air at 25°C is 1.6 ×10^–2, what is the concentration of O₃?

Predict which of the following reaction will have appreciable concentration of reactants and products:

a) 

b) 

c) 

The first ionization constant of H_2­­S is 9.1 x 10^-8. Calculate the concentration of HS^- ion in its 0.1 M solution. How will this concentration be affected if the solution is 0.1 M in HCl also? If the second dissociation constant of H₂S is 1.2 x 10^-13, calculate the concentration of S^2- under both conditions.

The ionization constant of phenol is 1.0 x 10^-10. What is the concentration of phenolate ion in 0.05 M solution of phenol? What will be its degree of ionization if the solution is also 0.01M in sodium phenolate?

The ionization constant of HF, HCOOH and HCN at 298K are 6.8 x 10^-4, 1.8 x 10^-4 and 4.8 x 10^-9 respectively. Calculate the ionization constants of the corresponding conjugate base.

The pH of a sample of vinegar is 3.76. Calculate the concentration of hydrogen ion in it.

The concentration of hydrogen ion in a sample of soft drink is 3.8 x 10^-3 M. what is its pH?

Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base: (a) OH^- (b) F^- (c) H⁺ (d) BCl₃.

At 473 K, equilibrium constant K_c for decomposition of phosphorus pentachloride, PCl₅ is 8.3 ×10^-3. If decomposition is depicted as,

 Δ_rH° = 124.0 kJmol^–1

a) Write an expression for K_c for the reaction.

b) What is the value of K_c for the reverse reaction at the same temperature?

c) What would be the effect on K_c if (i) more PCl₅ is added (ii) pressure is increased? (iii) The temperature is increased?

Describe the effect of:

a) Addition of H2

b) Addition of CH3OH

c) Removal of CO

d) Removal of CH3OH

on the equilibrium of the reaction:

Dihydrogen gas is obtained from natural gas by partial oxidation with steam as per following endothermic reaction:

(a) Write as expression for Kp for the above reaction.

(b) How will the values of Kp and composition of equilibrium mixture be affected by

(i) Increasing the pressure

(ii) Increasing the temperature

(iii) Using a catalyst?

The equilibrium constant for the following reaction is 1.6 ×105 at 1024 K.

 Find the equilibrium pressure of all gases if 10.0 bar of HBr is introduced into a sealed container at 1024 K.

Which of the following reactions will get affected by increasing the pressure?

Also, mention whether change will cause the reaction to go into forward or backward direction.

(i) 

(ii) 

(iii) 

(iv) 

(v) 

(vi) 

Does the number of moles of reaction products increase, decrease or remain same when each of the following equilibria is subjected to a decrease in pressure by increasing the volume?

(a) 

(b) 

(c) 

Calculate a) ΔG°and b) the equilibrium constant for the formation of NO₂ from NO and O₂ at 298 K

 where Δ_fG° (NO₂) = 52.0 kJ/mol

Δ_fG° (NO) = 87.0 kJ/mol

Δ_fG° (O₂) = 0 kJ/mol

At 1127 K and 1 atm pressure, a gaseous mixture of CO and CO₂ in equilibrium with solid carbon has 90.55% CO by mass

 Calculate K_c for this reaction at the above temperature.

Bromine monochloride, BrCl decomposes into bromine and chlorine and reaches the equilibrium:

for which Kc= 32 at 500 K. If initially pure BrCl is present at a concentration of 3.3 × 10–3 molL–1, what is its molar concentration in the mixture at equilibrium?

Equilibrium constant, K_c for the reaction

at 500 K is 0.061.

at 500 K is 0.061.

At a particular time, the analysis shows that composition of the reaction mixture is 3.0 mol L^–1 N₂, 2.0 mol L^–1H₂ and 0.5 mol L^–1 NH₃. Is the reaction at equilibrium? If not in which direction does the reaction tend to proceed to reach equilibrium?

One of the reactions that takes place in producing steel from iron ore is the reduction of iron (II) oxide by carbon monoxide to give iron metal and CO₂.

FeO (s) + CO (g)  Fe (s) + CO₂ (g); K_p= 0.265 at 1050 K.

What are the equilibrium partial pressures of CO and CO₂ at 1050 K if the initial partial pressures are: p_CO = 1.4 atm and = 0.80 atm?

A sample of pure PCl5 was introduced into an evacuated vessel at 473 K. After equilibrium was attained, concentration of PCl5 was found to be 0.5 × 10–1 mol L–1. If value of Kc is 8.3 × 10–3, what are the concentrations of PCl3 and Cl2 at equilibrium?

Ethyl acetate is formed by the reaction between ethanol and acetic acid and the equilibrium is represented as:

(i) Write the concentration ratio (reaction quotient), Qc, for this reaction (note: water is not in excess and is not a solvent in this reaction)

(ii) At 293 K, if one starts with 1.00 mol of acetic acid and 0.18 mol of ethanol, there is 0.171 mol of ethyl acetate in the final equilibrium mixture. Calculate the equilibrium constant.

(iii) Starting with 0.5 mol of ethanol and 1.0 mol of acetic acid and maintaining it at 293 K, 0.214 mol of ethyl acetate is found after sometime. Has equilibrium been reached?

K_p = 0.04 atm at 899 K for the equilibrium shown below. What is the equilibrium concentration of C₂H₆when it is placed in a flask at 4.0 atm pressure and allowed to come to equilibrium?

What is the equilibrium concentration of each of the substances in the equilibrium when the initial concentration of ICl was 0.78 M?

2 ICl(g) ⇌  I₂(g) + Cl₂(g) ; K_C = 0.14

 At 700 K, equilibrium constant for the reaction          

is 54.8. If 0.5 molL^–1 of HI_(g) is present at equilibrium at 700 K, what are the concentration of H_2(g) and I_2(g)assuming that we initially started with HI_(g) and allowed it to reach equilibrium at 700 K?

One mole of H₂O and one mole of CO are taken in 10 L vessel and heated to

725 K. At equilibrium 40% of water (by mass) reacts with CO according to the equation,

Calculate the equilibrium constant for the reaction.

The equilibrium constant expression for a gas reaction is,

Write the balanced chemical equation corresponding to this expression.

A mixture of 1.57 mol of N₂, 1.92 mol of H₂ and 8.13 mol of NH₃ is introduced into a 20 L reaction vessel at 500 K. At this temperature, the equilibrium constant, K_c for the reaction  

Is the reaction mixture at equilibrium? If not, what is the direction of the net reaction?

A sample of HI_(g) is placed in flask at a pressure of 0.2 atm. At equilibrium the partial pressure of HI_(g) is 0.04 atm. What is K_p for the given equilibrium?

At 450 K, K_p= 2.0 × 10¹⁰/bar for the given reaction at equilibrium.

What is K_c at this temperature?

Nitric oxide reacts with Br₂ and gives nitrosyl bromide as per reaction given below:

Nitric oxide reacts with Br2 and gives nitrosyl bromide as per reaction given below:                                                                                                                                                  

When 0.087 mol of NO and 0.0437 mol of Br₂ are mixed in a closed container at constant temperature, 0.0518 mol of NOBr is obtained at equilibrium. Calculate equilibrium amount of NO and Br₂.

Reaction between N₂ and O₂ takes place as follows:

If a mixture of 0.482 mol of N₂ and 0.933 mol of O₂ is placed in a 10 L reaction vessel and allowed to form N₂O at a temperature for which K_c = 2.0 × 10^–37, determine the composition of equilibrium mixture.

b

Explain why pure liquids and solids can be ignored while writing the equilibrium constant expression?

For the following equilibrium, 

Both the forward and reverse reactions in the equilibrium are elementary bimolecular reactions. What is Kc, for the reverse reaction?

Find out the value of K_c for each of the following equilibria from the value of K_p:

Write the expression for the equilibrium constant, Kc for each of the following

reactions:

(i) 

(ii) 

(iii) 

(iv) 

(v) 

At a certain temperature and total pressure of 10⁵ Pa, iodine vapour contains 40% by volume of I atoms

Calculate K_pfor the equilibrium.

What is K_c for the following equilibrium when the equilibrium concentration of each substance is: [SO₂]= 0.60 M, [O₂] = 0.82 M and [SO₃] = 1.90 M ?  

A liquid is in equilibrium with its vapour in a sealed container at a fixed temperature. The volume of the container is suddenly increased.

a) What is the initial effect of the change on vapour pressure?

b) How do rates of evaporation and condensation change initially?

c) What happens when equilibrium is restored finally and what will be the final vapour pressure?