Test Session Chapter 8 Chemical Equilibrium (1st Year Chemistry)

Q1. Choose the correct option. (10×1=10)

Consider the gas-phase equilibrium system represented by the equation:

2H₂O(g) ⇌ 2H₂(g) + O₂(g)

Given that the forward reaction is endothermic, which of the following changes will decrease the equilibrium amount of H₂O?

(A) Adding more oxygen

(B) Adding a solid phase catalyst

(D) Increasing the temperature at constant pressure

At dynamic equilibrium, the rate of:

(A) Forward reaction is zero

(B) Reverse reaction is zero

(D) Product formation is maximum

Which of the following statements is true about equilibrium constant?

(A) It depends on initial concentration

(B) It is constant at a given temperature

(D) It is zero for reversible reactions

If we start with only products in a reversible reaction, equilibrium:

(A) Will not be established

(B) Will still be reached

(D) Depends only on pressure

If the concentration of products is high at equilibrium, then Kc is:

(A) Very low

(B) Undefined

(D) High

Le-Chatelier’s Principle deals with:

(A) Rate of reaction

(B) Shifts in equilibrium due to disturbances

(D) Chemical bonding

When heat is added to an endothermic equilibrium, the reaction:

(A) Shifts forward

(B) Shifts backward

(D) Is destroyed

The only factor that affects the value of Kc is:

(A) Pressure

(B) Catalyst

(D) Temperature

What is the effect of catalyst on the equilibrium position?

(A) No effect

(B) Shifts to left

(D) Increase Kc

A catalyst works by:

(A) Increasing temperature

(B) Lowering activation energy

(D) Increasing concentration

Q2. Write down short answers of following questions. (14×2=28)

[I] Why can’t microscopic events be observed directly?

[II] Explain with examples how bond formation is a microscopic event.

[III] Why does a reversible reaction never stop?

[IV] Explain why dynamic equilibrium is not static in nature.

[V] What is the effect of catalyst on equilibrium?

[VI] Explain why equilibrium can be approached from both sides.

[VII] Why are pure solids not included in the Kc expression?

[VIII] Define heterogeneous equilibrium.

[IX] Define equilibrium constant.

[x] Does a change in concentration affect the value of Kc?

[xi] How does removal of product affect the equilibrium system?

[xii] What is the effect of adding a catalyst on a system at equilibrium?

[xiii] What is the effect of increasing temperature on an exothermic reaction?

[xiv] Describe the effect of temperature on Kc using SO₂ + O₂ ⇌ SO₃ example.

[xv] Give one example of a reaction affected by pressure.

Q3. Write detailed answers of the following questions. (Answer any 2) (2×5=10)

1. Define and explain the law of mass action and derive the expression for the equilibrium constant.

2. Write the expressions for Kc for the following reactions:

(i) Sn²⁺(aq) + 2Fe³⁺(aq) ⇌ Sn⁴⁺(aq) + 2Fe²⁺(aq)

(ii) Ag⁺(aq) + Fe²⁺(aq) ⇌ Fe³⁺(aq) + Ag(s)

(iii) N₂(g) + O₂(g) ⇌ 2NO(g)

(iv) 4NH₃(g) + 5O₂(g) ⇌ 4NO(g) + 6H₂O(g)

(v) PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)

3. Write down the Kc for the following reactions. Suppose that the reaction mixture in all the case is V′ dm⁻³.

(i) CH₃COOH + CH₃CH₂OH ⇌ CH₃COOC₂H₅ + H₂O

(ii) 2HI ⇌ H₂ + I₂

(iii) N₂ + 3H₂ ⇌ 2NH₃

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