Matric Notes Chemistry 10th Chapter 9 Chemical Equilibrium Exercise Short Questions

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Exercise Short Questions.

Q1. What are irreversible reactions? Give a few characteristics of them.

Ans. The reactions in which products do not recombine to form reactants are called irreversible reactions.

Characteristics:

1. These reaction proceed in one direction only.
2. These are represented by a single arrow (->) between reactants and products.
3. Reactants are completely converted into products at the end of reaction.

Q2. Define chemical equilibrium state.

Ans. When the rate of the forward reaction takes place at the rate of reverse reaction, the composition of the reaction mixture remains constant; it is called a chemical equilibrium state.

Q3. Give the characteristics of reversible reactions.

Ans. The reactions in which products react to produce reactants are called reversible reactions.

1. These reactions never go to completion.
2. They are represented by a double arrow ⇌ between reactants and products.
3. These reactions proceed in both ways; forward and reverse until they attain dynamic equilibrium state.

Q4. How is dynamic equilibrium established?

Ans. "Dynamic equilibrium is established when reaction does not stop, only the rates of forward and reverse reactions become equal to each other but take place in opposite direction." In a reversible reaction, dynamic equilibrium is established before the completion of reaction.

Q5. Why at equilibrium state reaction does not stop?

Ans. At equilibrium state the reaction does not stop because the rate of forward reaction is exactly equal to that of the reverse reaction but in opposite direction.

Q6. Why is equilibrium state attainable from either way?

Ans. An equilibrium state is attainable from either way because it may start from reactants to give products or products can react to give reactants.

Reactants ⇌ Products

Q7. What is the relationship between active mass and rate of reaction?

Ans. According to Guldberg and Waage's law of Mass Action, the rate of reaction is directly proportional to the product of the active mass of the reacting substances. i.e.

Rate of reaction ∝ Active masses of reaction substance.

Q8. Derive equilibrium constant expression for the synthesis of ammonia from nitrogen and hydrogen.

Ans. For the reaction of nitrogen with hydrogen to form ammonia, the balanced chemical equation if:

N₂ + 3H₂ ⇌ 2NH₃

For the reaction

The rate of forward reaction

(R_f) = k_f[N₂][H₂]³

The rate of reverse reaction

(R_r) = k_r[NH₃]²

At equilibrium R_f = R_r

k_f[N₂][H₂]³ = k_r[NH₃]²

k_f / k_r = [NH₃]² / [N₂][H₂]³

The expression for the equilibrium constant for this reaction is:

Kc = [NH₃]² / [N₂][H₂]³

Q9. Write the equilibrium constant expression for the following reactions:

i. H₂ + I₂ ⇌ 2HI

ii. CO + 3H₂ ⇌ CH₄ + H₂O

Ans. The equilibrium constant expression for these reactions is :

i. Kc = [HI]² / [H₂][I₂]

ii. Kc = [CH₄] [H₂O] / [CO][H₂]³

Q10. How can direction of a reaction be predicted?

Ans. Direction of a reaction at a particular moment can be predicted by comparing the value of Q_c with K_c.

• If Q_C < K_C; the reaction goes from left to right, i.e. in forward direction to attain equilibrium.
• If Q_C > K_C; the reaction goes from right to left, i.e. in reverse direction to attain equilibrium.
• If Q_C = K_C; forward and reverse reactions take place at equal rates i.e. equilibrium has been attained.

Q11. How can you know that a reaction has achieved an equilibrium state?

Ans. If Q_C = K_C , it indicates that forward and reverse reactions are taking place at equal rates, i.e. equilibrium has been attained.

Q12. What are the characteristics of a reaction that establishes equilibrium state at once?

Ans. The reactions which attains the equilibrium are called reversible reactions.

1. In these reactions dynamic state of equilibrium is established with very small conversion of reactants to products.
2. These reaction never go to completion.
3. They proceed in both directions.
4. For these reactions, value of 'K_C' is small.

Q13. If reaction quotient Q_C of a reaction is more than K_C. What will be the direction of the reaction?

Ans. If Q_C of a reaction is more than 'K_C' the reaction goes from right to left, i.e. in reverse direction.

Q14. An industry was established based upon a reversible reaction. It failed to achieve products commercial level. Can you point out the basic reasons of its failure being a chemist?

Ans. Industry established on the basis of a reversible reaction fails because reaction is reversible in which dynamic equilibrium is established between reactants and products. Products recombine to form the reactants so desired commercial product and required amount is not obtained.