Master Chemical Equilibrium: 🌡️💡 Explore Exam-Favorite MCQs to Ace Your Chemistry Exam!

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🔥🌿Master Chemical Equilibrium: 🌡️💡 Explore Exam-Favorite MCQs to Ace Your Chemistry Exam! ⚛️📘

1️⃣ Which one of the following statements is FALSE about dynamic equilibrium?

🟦 A) Concentration of reactant and products are not changed

🟩 B) It takes place in a closed container

🟪 C) Rate of forward reaction is equal to rate of reverse reaction

🟨 D) Equilibrium cannot be disturbed by any external stress

2️⃣ When the magnitude of Kc is small, it indicates:

🟦 A) Reaction mixture contains most of the reactant

🟩 B) Reaction mixture contains most of the product

🟪 C) Reaction mixture contains almost equal amount of reactant and product

🟨 D) Reaction goes to completion

3️⃣ Qc can be defined as:

🟦 A) Ratio of product and reactant

🟩 B) Ratio of molar concentration of product and reactant at specific time

🟪 C) Ratio of molar concentration of product and molar volume of reactant

🟨 D) Ratio of molar concentration of product and reactant raised to the power of coefficient

4️⃣  Consider the following reaction and indicate which of the following best describes the equilibrium constant expression Kc.

 4NH₃(g) + 5O₂(g) ⇌ 4NO(g) + 6H₂O(g)

🟦 A) [NO]⁴[H₂O]⁶ / [NH₃]⁴[O₂]⁵

🟩 B) [NH₃]⁴[O₂]⁵ / [NO]⁴[H₂O]⁶

🟪 C) [NH₃]¹[O₂]² / [NO]¹[H₂O]²

🟨 D) [NO]²[H₂O]³ / [NH₃]³[O₂]⁴

5️⃣  For which system does the equilibrium constant, Kc have units of concentration?

🟦 A) N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

🟩 B) N₂(g) + O₂(g) ⇌ 2NO(g)

🟪 C) H₂(g) + I₂(g) ⇌ 2HI(g)

🟨 D) CO₂(g) + H₂(g) ⇌ CO(g) + H₂O(g)

6️⃣ A reaction which never goes to completion is known as a reversible reaction. Reversible reactions are represented by:

🟦 A) Double straight line

🟩 B) Single arrow

🟪 C) Double arrow

🟨 D) Dotted lines

7️⃣  The unit of Kc for the reaction: N₂(g) + O₂(g) ⇌ 2NO(g)

🟦 A) mol dm⁻³

🟩 B) mol⁻² dm⁶

🟪 C) mol⁻¹ dm³

🟨 D) No unit

8️⃣ The system is stable in equilibrium when:

🟦 A) Qc = Kc

🟩 B) Qc > Kc

🟪 C) Qc < Kc

🟨 D) None of these

9️⃣ The value of Kc increases when:

🟦 A) [Reactant] = [product]

🟩 B) [Product] is more

🟪 C) [Reactant] is more

🟨 D) [Product] is less

🔟  Which of the following represents the backward reaction?

🟦 A) (i) and (ii)

🟩 B) (ii) only

🟪 C) (i) only

🟨 D) (iii) only

1️⃣1️⃣  A chemical reaction is at equilibrium when:

🟦 A) Rate of forward reaction > Rate of reverse reaction

🟩 B) Rate of forward reaction < Rate of reverse reaction

🟪 C) Rate of forward reaction = Rate of reverse reaction

🟨 D) All of the above

1️⃣2️⃣ In a chemical reaction, equilibrium is said to have been established when:

🟦 A) Concentration of reactants and products are equal

🟩 B) Velocities of opposing reactions become equal

🟪 C) Temperature of opposing reactions are equal

🟨 D) Opposing reactions cease.

1️⃣3️⃣ A chemical reaction A ⇌ B is said to be in equilibrium when:

🟦 A) Complete conversion of A to B has taken place

🟩 B) Complete conversion of A to B is only 50% complete

🟪 C) Only 10% conversion of A to B has taken place

🟨 D) The rate of transformation of A to B is just equal to the rate of transformation of B to A in the system.

1️⃣4️⃣ Which of the following statement is WRONG regarding chemical equilibrium?

🟦 A) At equilibrium two opposing chemical reactions are proceeding in opposite directions at different rates

🟩 B) At equilibrium there is no change in the concentration of reactant and product

🟪 C) Chemical equilibrium is always dynamic

🟨D) Chemical equilibrium can be disturbed by changing conditions like concentration, pressure, temperature

1️⃣5️⃣ Which one of the following is NOT a reversible reaction?

🟦 A) Oxidation of SO₂ into SO₃

🟩 B) Decomposition of potassium chlorate

🟪 C) Decomposition of Hydrogen Iodide

🟨 D) Formation of Ammonia from its constituent elements or Esterification

1️⃣6️⃣ Which one is INCORRECT regarding Kc?

🟦 A) It is a ratio between two rate constants and it has no unit when Δn = 0

🟩 B) It remains constant at all temperatures

🟪 C) It is independent of the pressure or catalyst

🟨 D) It is independent of the original concentration of reactants

1️⃣7️⃣  The value of Kc that lies midway between 10⁻² to 10² indicates that:

🟦 A) Forward reaction goes to completion

🟩 B) Reverse reaction goes to completion

🟪 C) Neither forward nor reverse reaction goes to completion

🟨 D) All of the above

1️⃣8️⃣  The value of Kc more than 10² indicates that:

🟦 A) Forward reaction goes to completion

🟩 B) Reverse reaction goes to completion

🟪 C) Neither forward nor reverse reaction goes to completion

🟨 D) All of the above

1️⃣9️⃣  The value of Kc less than 10⁻² indicates that:

🟦 A) Forward reaction goes to completion

🟩 B) Reverse reaction goes to completion

🟪 C) Neither forward nor reverse reaction goes to completion

🟨 D) All of the above

2️⃣0️⃣ Which one of the following factors will favor the reverse change?

🟦 A) Increase in concentration of one of the reactants

🟩 B) Removal of the products regularly

🟪 C) Increase in concentration of any one of the products

🟨 D) None of the above

2️⃣1️⃣  When H₂ and I₂ are mixed and equilibrium is attained, then:

🟦 A) The reaction stops completely

🟩 B) HI dissociates completely

🟪 C) Amount of HI formed is equal to the amount of HI dissociated

🟨 D) None of these

2️⃣2️⃣  Which of the following is a characteristic of a reversible reaction?

🟦 A) It never proceeds to completion

🟩 B) It can be influenced by a catalyst

🟪 C) It proceeds only in the forward direction

🟨 D) Number of moles of reactants and products are equal

2️⃣3️⃣At equilibrium, __________.

🟦 A) The rates of the forward and reverse reactions are equal

🟩 B) The rate constants of the forward and reverse reactions are equal

🟪 C) All chemical reactions have ceased

🟨 D) All of them

2️⃣4️⃣ How is the reaction quotient used to determine whether a system is at equilibrium?

🟦 A) The reaction is at equilibrium when Q < Keq

🟩 B) The reaction is at equilibrium when Q > Keq

🟪 C) At equilibrium, the reaction quotient is undefined

🟨 D) The reaction is at equilibrium when Q = Keq

2️⃣5️⃣  The equilibrium constant in a reversible chemical reaction at a given temperature:

🟦 A) Depends on the initial concentration of the reactants

🟩 B) Depends on the concentration of one of the products at equilibrium

🟪 C) Does not depend on the initial concentration of reactants

🟨 D) Is not characteristic of the reaction

2️⃣6️⃣  When a system is at equilibrium, it states:

🟦 A) The concentration of reactants and products becomes equal

🟩 B) The opposing reactions (forward and reverse) stop

🟪 C) Active mass is represented by small brackets

🟨 D) Active mass of all reacting species becomes constant

2️⃣7️⃣  Which one of the following statement is NOT correct about active mass?

🟦 A) Rate of reaction is directly proportional to active mass

🟩 B) Active mass is taken in molar concentration

🟪 C) Active mass is represented by square brackets

🟨 D) Active mass of all reacting species at equilibrium becomes equal

2️⃣8️⃣ The characteristics of reversible reactions are the following except:

🟦 A) Products never recombine to form reactants

🟩 B) They never complete

🟪 C) They proceed in both ways

🟨 D) They have a double arrow between reactants and products

2️⃣9️⃣  When the magnitude of Kc is very large it indicates:

🟦 A) Reaction mixture consists of almost all products

🟩 B) Reaction mixture has almost all reactants

🟪 C) Reaction has not gone to completion

🟨 D) Reaction mixture has negligible products

3️⃣0️⃣ When the magnitude of Kc is very small it indicates:

🟦 A) Equilibrium will never establish

🟩 B) All reactants will be converted into products

🟪 C) Reaction will go to completion

🟨 D) The amount of products is negligible

3️⃣1️⃣  Phosphorus reacts with chlorine according to the following equation:

 P₄(s) + 6Cl₂(g) ⇌ 4PCl₃(g)

What is the equilibrium constant, Kc, for the reaction?

🟦 A) Kc = ([Cl₂]⁶) / ([PCl₃]⁴)

🟩 B) Kc = ([P₄][Cl₂]⁶) / ([PCl₃]⁴)

🟪 C) Kc = ([PCl₃]⁴) / ([Cl₂]⁶)

🟨 D) Kc = ([PCl₃]) / ([Cl₂]⁶)

3️⃣2️⃣  For a reaction of the type; A(s) + 2B(g) ⇌ C(g); an equilibrium mixture consists of 3.0 moles of A, 0.80 moles of B, and 0.40 moles of C in a 2.00 L flask. What is the value of Kc for this reaction?

🟦 A) 5.0 x 10⁻¹

🟩 B) 8.3 x 10⁻¹

🟪 C) 1.25

🟨 D) 1.7 x 10⁻¹

3️⃣3️⃣ What is the equilibrium expression for the following reaction?

 CuSO₄(s) + 5H₂O(g) ⇌ CuSO₄.5H₂O(s)

🟦 A) Kc = ([CuSO₄][H₂O]⁵) / ([CuSO₄.5H₂O])

🟩 B) Kc = ([CuSO₄.5H₂O]) / ([CuSO₄][H₂O]⁵)

🟪 C) Kc = [H₂O]⁵

🟨 D) Kc = 1 / ([H₂O]⁵)

3️⃣4️⃣ The reaction which never goes to completion is called:

🟦 A) Exothermic reaction

🟩 B) Endothermic reaction

🟪 C) Reversible reaction

🟨 D) Irreversible reaction

3️⃣5️⃣  The rate at which substances react is directly proportional to its active mass and the rate of chemical reaction is proportional to the product of active masses of the reacting substances. It is called:

🟦 A) Law of mass action

🟩 B) Rate Law

🟪 C) Hess’s law

🟨 D) None of them

3️⃣6️⃣ In Kc expression, the active masses of __________ appear in numerator:

🟦 A) Products

🟩 B) Reactants

🟪 C) Catalyst

🟨 D) None of them

3️⃣7️⃣  In Kc expression, the active masses of __________ appear in denominator:

🟦 A) Products

🟩 B) Reactants

🟪 C) Catalyst

🟨 D) None of them

3️⃣8️⃣  In which of the following cases does the reaction go farthest to completion?

🟦 A) Kc = 10²

🟩 B) Kc = 10⁻²

🟪 C) Kc = 10

🟨 D) Kc = 1

3️⃣9️⃣  In which of the following cases does the reaction not go farthest to completion?

🟦 A) Kc = 10²

🟩 B) Kc = 10⁻²

🟪 C) Kc = 10

🟨 D) Kc = 1

4️⃣0️⃣  A catalyst speeds up the rate of __________ reaction.

🟦 A) Forward

🟩 B) Backward

🟪 C) Both forward and backward

🟨 D) None of them

4️⃣1️⃣  The reaction between alcohol and acid is called:

🟦 A) Hydrolysis

🟩 B) Neutralization

🟪 C) Saponification

🟨 D) Esterification

4️⃣2️⃣  For a reversible reaction, if the concentration of both the reactants are doubled, then the equilibrium constant is:

🟦 A) Also doubled

🟩 B) Halved

🟪 C) Quadrupled

🟨 D) Not changed

4️⃣3️⃣  The value of Kc does not depend on _______.

🟦 A) Temperature

🟩 B) Initial concentration

🟪 C) Both of them

🟨 D) None of them

4️⃣4️⃣ If Kc is very large, then the reaction is considered to be ___________.

🟦 A) Reversible

🟩 B) Irreversible

🟪 C) Exothermic

🟨 D) None of them

4️⃣5️⃣  In a reversible chemical reaction having two reactants in equilibrium, if the concentration of the reactants is doubled, then the equilibrium constant will:

🟦 A) Also be doubled

🟩 B) Remain the same

🟪 C) Become one fourth

🟨 D) Be halved

4️⃣6️⃣ For the reaction, A + B ⇌ C, the equilibrium constant unit is:

🟦 A) dm³ mol⁻

🟩 B) mol dm⁻³

🟪 C) mol dm³

🟨 D) mol² dm⁻³

4️⃣7️⃣ The reaction in which the products do not recombine to form reactants are called:

🟦 A) Reversible reactions

🟩 B) Irreversible reactions

🟪 C) Decomposition

🟨 D) Addition

4️⃣8️⃣ The reaction in which the products can recombine to form reactants are called:

🟦 A) Reversible reactions

🟩 B) Irreversible reactions

🟪 C) Decomposition

🟨 D) Addition

4️⃣9️⃣ The color of iodine is:

🟦 A) Purple

🟩 B) Black

🟪 C) Red

🟨 D) Pink

5️⃣0️⃣  The color of hydrogen iodide is:

🟦 A) Colorless

🟩 B) Black

🟪 C) Red

🟨 D) Pink

5️⃣1️⃣  When the rate of the forward reaction takes place at the rate of reverse action, the composition of the reaction mixture remains constant, it is called:

🟦 A) Static equilibrium

🟩 B) Dynamic equilibrium

🟪 C) Chemical equilibrium

🟨 D) All

5️⃣2️⃣ Guldberg and Waage put forward the law of mass action in:

🟦 A) 1860

🟩 B) 1864

🟪 C) 1870

🟨 D) 1879

5️⃣3️⃣  The percentage of nitrogen and oxygen in our atmosphere is:

🟦 A) 80

🟩 B) 90

🟪 C) 95

🟨 D) 99

5️⃣4️⃣ Which gas is used to prepare ammonia?

🟦 A) N₂

🟩 B) O₂

🟪 C) Cl₂

🟨 D) S

5️⃣5️⃣  Which gas is used to manufacture the king of chemicals, sulphuric acid?

🟦 A) N₂

🟩 B) O₂

🟪 C) Cl₂

🟨 D) SO₂

5️⃣6️⃣  Equilibrium constant has no unit when the number of moles of reactants and products are:

🟦 A) Same

🟩 B) Different

🟪 C) Both A & B

🟨 D) None

5️⃣7️⃣ For reactions having a large Kc value, the reaction proceeds to:

🟦 A) Completion

🟩 B) Equilibrium state

🟪 C) Backward

🟨 D) None

5️⃣8️⃣  For the reaction, 2A(g) + B(g) ⇌ 3C(g), the expression for the equilibrium constant is:

🟦 A) [2A][B] / [3C]

🟩 B) [A]²[B] / [C]³

🟪 C) [3C] / [2A][B]

🟨 D) [C]³ / [A]²[B]

5️⃣9️⃣  Reactions which have comparable amounts of reactants and products at equilibrium state have:

🟦 A) Very small Kc value

🟩 B) Very large Kc value

🟪 C) Moderate Kc value

🟨 D) None of these

6️⃣0️⃣Nitrogen and hydrogen were reacted together to make ammonia:

 N₂ + 3H₂ ⇌ 2NH₃, Kc = 2.86 mol⁻² dm⁶. What will be present in the equilibrium mixture?

🟦 A) NH₃ only

🟩 B) N₂, H₂, and NH₃

🟪 C) N₂ and H₂

🟨 D) H₂ only

6️⃣1️⃣  For a reaction between PCl₃ and Cl₂ to form PCl₅, the units of Kc are:

🟦 A) mol dm⁻³

🟩 B) mol⁻¹ dm⁻³

🟪 C) mol⁻¹ dm³

🟨 D) mol dm³

6️⃣2️⃣  The two major components of the atmosphere are:

🟦 A) Carbon and nitrogen

🟩 B) Nitrogen and oxygen

🟪 C) Oxygen and chlorine

🟨 D) None of these

6️⃣3️⃣  Which type of reactions do not go to completion?

🟦 A) Irreversible reaction

🟩 B) Reversible reactions

🟪 C) Addition reactions

🟨 D) Decomposition

6️⃣4️⃣ Which type of reaction speeds up gradually?

🟦 A) Irreversible reaction

🟩 B) Reversible reactions

🟪 C) Addition reactions

🟨 D) Decomposition

6️⃣5️⃣ Which type of reactions take place in both directions?

🟦 A) Addition reactions

🟩 B) Reversible reactions

🟪 C) Irreversible reactions

🟨 D) Decomposition

6️⃣6️⃣  In a chemical reaction, the substances that combine are called:

🟦 A) Reactants

🟩 B) Products

🟪 C) Mass

🟨 D) Material

6️⃣7️⃣  Dynamic means, reaction is:

🟦 A) In forward direction

🟩 B) Still continuing

🟪 C) In reverse direction

🟨 D) Stopped

6️⃣8️⃣  The forward reaction takes place:

🟦 A) Right to left

🟩 B) Left to right

🟪 C) Only to right

🟨 D) Only to left

6️⃣9️⃣  The units of molar concentration are:

🟦 A) mol·dm⁻²

🟩 B) mol·dm⁻¹

🟪 C) mol·dm

🟨 D) mol·dm⁻³

7️⃣0️⃣  The equilibrium constant value "Kc" is equal to:

🟦 A) Kf / Kr

🟩 B) Kr / Kf

🟪 C) Kc / Qc

🟨 D) Qc / Kr

7️⃣1️⃣  Which chemical is called the king of chemicals?

🟦 A) KNO₃

🟩 B) H₂SO₄

🟪 C) HCl

🟨 D) HNO₃

7️⃣2️⃣ The rate at which substances react is directly proportional to its active mass, and the rate of chemical reaction is proportional to the product of active masses of the reacting substances. It is called:

🟦 A) Law of mass action

🟩 B) Rate Law

🟪 C) Hess’s law

🟨 D) None of them

7️⃣3️⃣  For a chemical reaction aA + bB ⇌ cC + dD, the Kc expression is written as:

🟦 A) [A]ⁿ [B]ᵐ / [C]ᶜ [D]ᵈ

🟩 B) [C]ᶜ [D]ᵈ / [A]ⁿ [B]ᵐ

🟪 C) [A] [B] / [C] [D]

🟨 D) [C] [D] / [A] [B]

7️⃣4️⃣  Using molar concentrations, what is the unit of Kc for the following reaction?

 CH₃OH(g) ⇌ CO(g) + 2H₂(g)

🟦 A) M⁻²

🟩 B) M²

🟪 C) M⁻¹

🟨 D) M

7️⃣5️⃣ What is the equilibrium expression for the reaction: P₄(s) + 5O₂(g) ⇌ P₄O₁₀(s)?

🟦 A) Kc = [O₂]⁵

🟩 B) Kc = [P₄O₁₀] / [P₄] [O₂]⁵

🟪 C) Kc = [P₄O₁₀] / [P₄] [O₂]

🟨 D) Kc = 1 / [O₂]⁵

7️⃣6️⃣  The reaction A(g) ⇌ B(g) has a Kc value of 4.1 x 10². At equilibrium, which of the following would be true?

🟦 A) [A] = [B]

🟩 B) [A] > [B]

🟪 C) [A] < [B]

🟨 D) Both A and B

7️⃣7️⃣  Which of the following expression of Kc is correct for the following reaction?

 N₂O₄ ⇌ 2NO₂

🟦 A) Kc = [N₂O₄] / [NO₂]²

🟩 B) Kc = [N₂O₄] / [NO₂]

🟪 C) Kc = [NO₂]² / [N₂O₄]

🟨 D) Kc = [NO₂] / [N₂O₄]

7️⃣8️⃣  Which of the following is the unit of Kc for the following reaction?

 N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

🟦 A) mol⁻² dm⁶

🟩 B) mol⁻¹ dm⁻³

🟪 C) mol⁻² dm³

🟨 D) No unit

7️⃣9️⃣ What is the equilibrium constant, Kc, for this reaction?

 CO₂(g) + 3H₂(g) ⇌ CH₃OH(g) + H₂O(g)

🟦 A) Kc = [CH₃OH] [H₂O] / [CO₂] [H₂]³

🟩 B) Kc = [CH₃OH] [H₂O] / [CO₂] [H₂]

🟪 C) Kc = [CO₂] [H₂]³ / [CH₃OH] [H₂O]

🟨 D) Kc = [CO₂] [H₂] / [CH₃OH] [H₂O]

8️⃣0️⃣ What is the equilibrium constant (Kc) for the given reaction?

2S(s) + 3O₂(g) ⇌ 2SO₃(g)

🟦 A) Kc = [SO₃] / [S] [O₂]³

🟩 B) Kc = [SO₃]² / [S] [O₂]³

🟪 C) Kc = [SO₃]² / [S]² [O₂]³

🟨 D) Kc = [SO₃]² / [O₂]³

8️⃣1️⃣  In the lime kiln, the reaction CaCO₃ → CaO + CO₂ goes to completion because:

🟦 A) Of high temperature

🟩 B) CaO is more stable than CaCO₃

🟪 C) CO₂ escapes continuously

🟨 D) CaO is not dissociated

8️⃣2️⃣  For a chemical reaction mA + nB ⇌ OC + pD, the Kc expression is written as:

🟦 A) ([A]ᵐ [B]ⁿ) / ([C]ᵒ [D]ᵖ)

🟩 B) ([C]ᵒ [D]ᵖ) / ([A]ᵐ [B]ⁿ)

🟪 C) [A] [B] / [C] [D]

🟨 D) [C] [D] / [A] [B]

8️⃣3️⃣  For a reaction 3A + 2B ⇌ C, the Kc expression is written as:

🟦 A) [A]³ [B]² / [C]c

🟩 B) [C] / [A]³ [B]²

🟪 C) [A]² [B]³ / [C]

🟨 D) [A]³ [B]³ / [C]²

8️⃣4️⃣ At dynamic equilibrium:

🟦 A) The reaction stops to proceed

🟩 B) The speed of the forward and reverse reactions are equal

🟪 C) The amount of reactants and products are equal

🟨 D) The reaction can no longer be reversed

8️⃣5️⃣ In an irreversible reaction, dynamic equilibrium:

🟦 A) Never establishes

🟩 B) Establishes before the completion of the reaction

🟪 C) Establishes after the completion of the reaction

🟨 D) Establishes readily

8️⃣6️⃣  A reverse reaction is one that:

🟦 A) Proceeds from left to right

🟩 B) In which the reactants react to form products

🟪 C) Slows down gradually

🟨 D) Speeds up gradually

🌟 Answer Key & Explanations 🌟

1️⃣ Answer: 🟨 D) Equilibrium cannot be disturbed by any external stress

Reason: Equilibrium can be disturbed by changes in concentration, pressure, or temperature according to Le Chatelier’s principle.

2️⃣ Answer: 🟦 A) Reaction mixture contains most of the reactant

Reason: A small Kc means the equilibrium favors the reactants, and not much product is formed.

3️⃣ Answer: 🟩 B) Ratio of molar concentration of product and reactant at specific time

Reason: Qc is the reaction quotient, calculated at any given moment to compare with the equilibrium constant, Kc.

4️⃣ Answer: 🟦 A) [NO]⁴[H₂O]⁶ / [NH₃]⁴[O₂]⁵

Reason: The equilibrium expression is formed by the concentrations of products raised to their coefficients, divided by the reactants in the same way.

5️⃣ Answer: 🟦 A) N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

Reason: Kc for reactions where the number of moles on both sides differs has units based on the change in moles, which leads to units of concentration.

6️⃣ Answer: 🟪 C) Double arrow

Reason: A reversible reaction is represented by a double arrow (⇌), showing that both the forward and reverse reactions occur.

7️⃣ Answer: 🟩 B) mol⁻² dm⁶

Reason: The unit for Kc depends on the reaction’s stoichiometry, and for this reaction, the units are mol⁻² dm⁶.

8️⃣ Answer: 🟦 A) Qc = Kc

Reason: At equilibrium, the reaction quotient (Qc) equals the equilibrium constant (Kc).

9️⃣ Answer: 🟦 A) [Reactant] = [product]

Reason: When the concentrations of reactants and products are equal, Kc increases, signaling equilibrium.

🔟 Answer: 🟩 B (ii) only

Reason: The backward reaction leads to give more products indicated by the more rounded dots (reactants) as compared to asterisk signs (products)

1️⃣1️⃣ Answer: 🟪 C) Rate of forward reaction = Rate of reverse reaction

Reason: Chemical equilibrium is established when the rates of the forward and reverse reactions are equal.

1️⃣2️⃣ Answer: 🟩 B) Velocities of opposing reactions become equal

Reason: Equilibrium occurs when the forward and reverse reaction rates are equal, but not necessarily when the concentrations are equal.

1️⃣3️⃣ Answer: 🟨 D) The rate of transformation of A to B is just equal to the rate of transformation of B to A in the system.

Reason: At equilibrium, the rates of both transformations (A ⇌ B) are equal.

1️⃣4️⃣ Answer: 🟦 A) At equilibrium two opposing chemical reactions are proceeding in opposite directions at different rates

Reason: At equilibrium, both the forward and reverse reactions are proceeding at the same rate.

1️⃣5️⃣ Answer: 🟨 D) Formation of Ammonia from its constituent elements or Esterification

Reason: Esterification is typically a reversible reaction, but the formation of ammonia from elements is not, it goes largely to completion.

1️⃣6️⃣ Answer: 🟪 C) It is independent of the pressure or catalyst

Reason: Kc is independent of the presence of catalysts and pressure, as long as the temperature remains constant.

1️⃣7️⃣ Answer: 🟪 C) Neither forward nor reverse reaction goes to completion

Reason: A Kc value between 10⁻² and 10² indicates that neither the forward nor the reverse reaction goes to completion.

1️⃣8️⃣ Answer: 🟦 A) Forward reaction goes to completion

Reason: When Kc > 10², the equilibrium favors the products, meaning the forward reaction goes to completion.

1️⃣9️⃣ Answer: 🟩 B) Reverse reaction goes to completion

Reason: A Kc value less than 10⁻² indicates that the equilibrium favors the reactants, and the reverse reaction goes to completion.

2️⃣0️⃣ Answer: 🟪 C) Increase in concentration of any one of the products

Reason: According to Le Chatelier’s principle, adding more product will shift the equilibrium to the left, favoring the reverse reaction.

2️⃣1️⃣ Answer: 🟨 D) None of these

Reason: At equilibrium, HI does not dissociate completely, and the reaction does not stop completely.

2️⃣2️⃣ Answer: 🟦 A) It never proceeds to completion

Reason: A reversible reaction does not go to completion and can establish equilibrium between reactants and products.

2️⃣3️⃣ Answer: 🟦 A) The rates of the forward and reverse reactions are equal

Reason: Equilibrium is reached when the rates of the forward and reverse reactions become equal.

2️⃣4️⃣ Answer: 🟨 D) The reaction is at equilibrium when Q = Keq

Reason: The reaction quotient (Q) equals the equilibrium constant (Keq) when the system is at equilibrium.

2️⃣5️⃣ Answer: 🟪 C) Does not depend on the initial concentration of reactants

Reason: The equilibrium constant (Kc) is independent of the initial concentrations of reactants, only dependent on temperature.

2️⃣6️⃣ Answer: 🟨 D) Active mass of all reacting species becomes constant

Reason: At equilibrium, the concentrations of reactants and products remain constant, but not necessarily equal.

2️⃣7️⃣ Answer: 🟨 D) Active mass of all reacting species at equilibrium becomes equal

Reason: Active mass refers to the molar concentration of a species, and these are not necessarily equal for all species at equilibrium.

2️⃣8️⃣ Answer: 🟦 A) Products never recombine to form reactants

Reason: In reversible reactions, products can recombine to form reactants, which is a characteristic of reversible reactions.

2️⃣9️⃣ Answer: 🟦 A) Reaction mixture consists of almost all products

Reason: A large Kc value indicates that the equilibrium favors the products, meaning the reaction mixture consists mostly of products.

3️⃣0️⃣ Answer: 🟨 D) The amount of products is negligible

Reason: A small Kc value indicates that the equilibrium favors the reactants, meaning the amount of products is negligible.

3️⃣1️⃣ Answer: 🟪 C) Kc = ([PCl₃]⁴) / ([Cl₂]⁶)

Reason: Pure solids and liquids do not appear in the Kc expression. Since P₄ is a solid, it is excluded from the equilibrium expression.

3️⃣2️⃣ Answer: 🟪 C) 1.25

Reason: Using the formula: Kc = [C] / [B]², we calculate:

Kc = (0.40/2) / (0.80/2)² = 0.2 / (0.40)² = 0.2 / 0.16 = 1.25

3️⃣3️⃣ Answer: 🟨 D) Kc = 1 / ([H₂O]⁵)

Reason: Concentrations of pure solids and liquids do not appear in Kc expression. Since CuSO₄ and CuSO₄.5H₂O are solids, only H₂O's concentration appears in the Kc expression.

3️⃣4️⃣ Answer: 🟪 C) Reversible reaction

Reason: A reversible reaction does not go to completion, as it can reach equilibrium where both forward and reverse reactions occur simultaneously.

3️⃣5️⃣ Answer: 🟦 A) Law of mass action

Reason: The law of mass action states that the rate of a reaction is proportional to the active masses (concentrations) of the reactants.

3️⃣6️⃣ Answer: 🟦 A) Products

Reason: In the equilibrium expression, the concentrations of products appear in the numerator.

3️⃣7️⃣ Answer: 🟩 B) Reactants

Reason: In the equilibrium expression, the concentrations of reactants appear in the denominator.

3️⃣8️⃣ Answer: 🟦 A) Kc = 10²

Reason: A very large Kc value indicates that the equilibrium favors the products, so the reaction proceeds farthest toward completion.

3️⃣9️⃣ Answer: 🟩 B) Kc = 10⁻²

Reason: A very small Kc value indicates that the equilibrium favors the reactants, so the reaction does not proceed farthest to completion.

4️⃣0️⃣ Answer: 🟪 C) Both forward and backward

Reason: A catalyst speeds up both the forward and reverse reactions by lowering the activation energy, but does not affect the equilibrium.

4️⃣1️⃣ Answer: 🟨 D) Esterification

Reason: The reaction between an alcohol and an acid to form an ester is known as esterification.

4️⃣2️⃣ Answer: 🟨 D) Not changed

Reason: The equilibrium constant (Kc) is dependent on temperature, but not on the concentrations of reactants or products.

4️⃣3️⃣ Answer: 🟩 B) Initial concentration

Reason: Kc is independent of the initial concentrations of reactants and products, but it is dependent on temperature.

4️⃣4️⃣ Answer: 🟩 B) Irreversible

Reason: A large Kc value indicates that the equilibrium lies far to the right, favoring the products, making the reaction nearly irreversible.

4️⃣5️⃣ Answer: 🟩 B) Remain the same

Reason: The equilibrium constant is independent of the concentration of reactants and products, so doubling the concentration does not change Kc.

4️⃣6️⃣ Answer: 🟦 A) dm³ mol⁻

Reason: The unit for the equilibrium constant (Kc) depends on the reaction stoichiometry. For the reaction A + B ⇌ C, the unit is dm³ mol⁻.

4️⃣7️⃣ Answer: 🟩 B) Irreversible reactions

Reason: Irreversible reactions do not go backward; once products are formed, they cannot recombine to form reactants.

4️⃣8️⃣ Answer: 🟦 A) Reversible reactions

Reason: Reversible reactions can proceed in both the forward and reverse directions.

4️⃣9️⃣ Answer: 🟦 A) Purple

Reason: Iodine is typically purple in color, especially in its gaseous form.

5️⃣0️⃣ Answer: 🟦 A) Colorless

Reason: Hydrogen iodide (HI) is a colorless gas.

5️⃣1️⃣ Answer: 🟩 B) Dynamic equilibrium

Reason: Dynamic equilibrium is when the forward and reverse reactions occur at the same rate, and the concentrations of reactants and products remain constant.

5️⃣2️⃣ Answer: 🟩 B) 1864

Reason: Guldberg and Waage formulated the law of mass action in 1864.

5️⃣3️⃣ Answer: 🟦 A) 80

Reason: The atmosphere consists of approximately 78% nitrogen and 21% oxygen, totaling around 99%.

5️⃣4️⃣ Answer: 🟦 A) N₂

Reason: Ammonia (NH₃) is primarily synthesized by reacting nitrogen (N₂) with hydrogen (H₂) in the Haber process.

5️⃣5️⃣ Answer: 🟨 D) SO₂

Reason: Sulphur dioxide (SO₂) is used in the production of sulphuric acid (H₂SO₄), often in the Contact Process.

5️⃣6️⃣ Answer: 🟦 A) Same

Reason: If the number of moles of reactants and products are the same, the equilibrium constant (Kc) has no units.

5️⃣7️⃣ Answer: 🟦 A) Completion

Reason: A very large Kc value indicates that the equilibrium strongly favors the products, meaning the reaction proceeds almost to completion.

5️⃣8️⃣ Answer: 🟨 D) [C]³ / [A]²[B]

Reason: The equilibrium expression is written as the concentration of products raised to their coefficients over the concentration of reactants raised to their coefficients: Kc = [C]³ / [A]²[B].

5️⃣9️⃣ Answer: 🟪 C) Moderate Kc value

Reason: A moderate Kc value indicates that there are comparable amounts of reactants and products at equilibrium.

6️⃣0️⃣ Answer: 🟩 B) N₂, H₂, and NH₃

Reason: With a Kc value of 2.86 mol⁻² dm⁶, this reaction is not at completion, so all three substances (N₂, H₂, and NH₃) will be present at equilibrium.

6️⃣1️⃣ Answer: 🟪 C) mol⁻¹ dm³

Reason: Kc has no unit when the total number of moles of reactants equals the total number of moles of products. The correct unit is mol⁻¹ dm³, based on the difference in the number of moles.

6️⃣2️⃣ Answer: 🟩 B) Nitrogen and oxygen

Reason: Nitrogen and oxygen are the two major components of Earth's atmosphere.

6️⃣3️⃣ Answer: 🟩 B) Reversible reactions

Reason: Reversible reactions do not go to completion, as they establish equilibrium between reactants and products.

6️⃣4️⃣ Answer: 🟩 B) Reversible reactions

Reason: Reversible reactions proceed in both directions, so the speed of the reaction changes gradually as equilibrium is approached.

6️⃣5️⃣ Answer: 🟩 B) Reversible reactions

Reason: Reversible reactions take place in both directions, and they can establish an equilibrium.

6️⃣6️⃣ Answer: 🟦 A) Reactants

Reason: In a chemical reaction, the substances that combine to form products are called reactants.

6️⃣7️⃣ Answer: 🟩 B) Still continuing

Reason: Dynamic equilibrium means that reactions are ongoing, but the rates of the forward and reverse reactions are equal, leading to no net change in the composition of the system.

6️⃣8️⃣ Answer: 🟩 B) Left to right

Reason: The forward reaction typically moves from left to right, converting reactants into products.

6️⃣9️⃣ Answer: 🟨 D) mol·dm⁻³

Reason: Molar concentration is measured in moles per liter, which is mol·dm⁻³.

7️⃣0️⃣ Answer: 🟦 A) Kf / Kr

Reason: The equilibrium constant, Kc, is the ratio of the rate constants of the forward (Kf) and reverse (Kr) reactions.

7️⃣1️⃣ Answer: 🟩 B) H₂SO₄

Reason: Sulfuric acid (H₂SO₄) is often referred to as the "king of chemicals" due to its wide range of industrial applications.

7️⃣2️⃣ Answer: 🟦 A) Law of mass action

Reason: The law of mass action relates the rate of a reaction to the active masses (concentrations) of the reactants.

7️⃣3️⃣ Answer: 🟩 B) [C]ᶜ [D]ᵈ / [A]ᵃ [B]ᵇ

Reason: The equilibrium expression is written as the concentration of products raised to their stoichiometric coefficients, divided by the reactants raised to their coefficients.

7️⃣4️⃣ Answer: 🟩 B) M²

Reason: The unit of Kc for this reaction is determined by the difference in the number of moles of products and reactants.

7️⃣5️⃣ Answer: 🟨 D) Kc = 1 / [O₂]⁵

Reason: The concentration of pure solids and liquids does not appear in the equilibrium expression, so only O₂ appears in the expression for this reaction.

7️⃣6️⃣ Answer: 🟪 C) [A] < [B]

Reason: A large Kc value indicates that the equilibrium lies towards the products, so the concentration of products (B) is higher than that of reactants (A).

7️⃣7️⃣ Answer: 🟪 C) Kc = [NO₂]² / [N₂O₄]

Reason: For the reaction N₂O₄ ⇌ 2NO₂, the correct Kc expression is written as the concentration of NO₂ squared (due to its coefficient) divided by the concentration of N₂O₄.

7️⃣8️⃣ Answer: 🟦 A) mol⁻² dm⁶

Reason: The unit of Kc depends on the difference in the total number of moles of products and reactants. For this reaction, the unit is mol⁻² dm⁶.

7️⃣9️⃣ Answer: 🟦 A) Kc = [CH₃OH][H₂O] / [CO₂][H₂]³

Reason: The equilibrium constant expression is based on the concentrations of the products over the reactants, with coefficients as exponents.

8️⃣0️⃣ Answer: 🟨 D) Kc = [SO₃]² / [O₂]³

Reason: Since S is a solid, it does not appear in the equilibrium expression, and the equilibrium constant depends on the concentrations of the gaseous species.

8️⃣1️⃣ Answer: 🟪 C) CO₂ escapes continuously

Reason: The escape of CO₂ from the reaction mixture favors the forward reaction, helping the reaction go to completion.

8️⃣2️⃣ Answer: 🟩 B) ([C]ᵒ [D]ᵖ) / ([A]ᵐ [B]ⁿ)

Reason: The equilibrium expression is written with products in the numerator and reactants in the denominator, with their coefficients as exponents.

8️⃣3️⃣ Answer: 🟩 B) [C] / [A]³ [B]²

Reason: For the reaction 3A + 2B ⇌ C, the equilibrium expression is written as [C] / [A]³ [B]², with the stoichiometric coefficients as powers of concentration.

8️⃣4️⃣ Answer: 🟩 B) The speed of the forward and reverse reactions are equal

Reason: At dynamic equilibrium, the rates of the forward and reverse reactions are equal, but both reactions continue to occur.

8️⃣5️⃣ Answer: 🟦 A) Never establishes

Reason: In an irreversible reaction, dynamic equilibrium does not occur because the reaction goes to completion in one direction.

8️⃣6️⃣ Answer: 🟩 B) In which the reactants react to form products

Reason: A reverse reaction is one in which the products can recombine to form the reactants, proceeding in the opposite direction.

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