Prepare for your 10th-grade exams with solved exercises on Chemical Equilibrium, following the PTB curriculum. Focus on concepts like Le Chatelier’s Principle, reaction rates, and equilibrium constants.
Short Questions:
1. What are irreversible reactions? Give a few characteristics of them?
Irreversible reactions are those in which reactants completely convert into products and cannot revert to their original form. Characteristics include:
- The reaction proceeds in one direction.
- The products do not revert to reactants.
- The reaction often goes to completion.
2. Define chemical equilibrium state.
Chemical equilibrium is the state in a reversible reaction where the rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant over time.
3. Give the characteristics of reversible reactions.
- Reversible reactions can proceed in both directions (forward and reverse).
- At equilibrium, the concentrations of reactants and products become constant.
- The reaction doesn’t stop; the forward and reverse rates are equal.
4. How is dynamic equilibrium established?
Dynamic equilibrium is established when the rate of the forward reaction becomes equal to the rate of the reverse reaction, and the concentrations of all reactants and products remain constant.
5. Why at equilibrium state reaction does not stop?
At equilibrium, the reaction doesn’t stop because both forward and reverse reactions continue at the same rate, resulting in no net change in concentrations.
6. Why is equilibrium state attainable from either way?
The equilibrium state is attainable from either side (reactants or products) because the system will adjust the rates of forward and reverse reactions to reach equilibrium, regardless of the starting conditions.
7. What is the relationship between active mass and rate of reaction?
The rate of a reaction is directly proportional to the active mass (concentration) of the reactants, as expressed in the law of mass action.
8. Derive equilibrium constant expression for the synthesis of ammonia from nitrogen and hydrogen.
For the reaction:
N2 + 3H2 ⇌ 2NH3
The equilibrium constant expression is:
Kc = [NH3]^2/[N2][H2]^3
9. Write the equilibrium constant expression for the following reactions:
i.
H2(g) + I2(g) ⇌ 2HI(g)
Kc = [HI]^2/[H2][I2]
ii.
CO(g) + 3H2(g) ⇌ CH4(g) + H2O(g)
Kc = [CH4][H2O]/[CO][H2]^3
10. How direction of a reaction can be predicted?
The direction of a reaction can be predicted by comparing the reaction quotient (Q) with the equilibrium constant (K).
- If ( Q < K ), the reaction will proceed forward.
- If ( Q > K ), the reaction will proceed in reverse.
11. How can you know that a reaction has achieved an equilibrium state?
A reaction has achieved equilibrium when the concentrations of reactants and products remain constant over time, and the rates of the forward and reverse reactions are equal.
12. What are the characteristics of a reaction that establishes equilibrium state at once?
Characteristics include:
- Constant concentrations of reactants and products.
- Equal rates for the forward and reverse reactions.
- No observable changes in the system without external disturbance.
- The reaction continues in both directions at equilibrium.
13. If reaction quotient Q, of a reaction is more than K, what will be the direction of the reaction?
If ( Q > K ), the reaction will shift in the reverse direction to re-establish equilibrium.
14. An industry was established based upon a reversible reaction. It failed to achieve products on a commercial level. Can you point out the basic reasons for its failure being a chemist?
Possible reasons for failure include:
- Incorrect reaction conditions (e.g., temperature, pressure) that are not optimized for equilibrium.
- The reaction not being conducted in a closed system, leading to loss of products.
- Poor choice of catalyst, affecting the reaction rate or equilibrium.
Extensive Questions:
1. Describe a reversible reaction with the help of an example and graph.
A reversible reaction can proceed in both the forward and reverse directions. For example, the reaction ( N2 + 3H2 ⇌ 2NH3 ) is reversible. In this reaction, both the reactants (nitrogen and hydrogen) and products (ammonia) coexist at equilibrium. The graph shows that the concentration of reactants and products stabilizes as equilibrium is established, where both the forward and reverse reactions continue at the same rate.
2. Write down the macroscopic characteristics of dynamic equilibrium.
The macroscopic characteristics of dynamic equilibrium include:
- Constant concentrations of reactants and products.
- No observable changes in the system, even though reactions continue at the microscopic level.
- Equal forward and reverse reaction rates.
3. State the law of Mass Action and derive the expression for equilibrium constant for a general reaction.
The law of Mass Action states that the rate of a reaction is proportional to the product of the concentrations of the reactants, each raised to the power of their respective stoichiometric coefficients. For a general reaction:
aA + bB ⇌ cC + dD
The equilibrium constant expression is:
Kc = [C]^c[D]^d/[A]^a[B]^b
4. What is the importance of equilibrium constant?
The equilibrium constant (K) provides valuable information about the position of equilibrium in a reaction. A large ( K ) value indicates that the reaction favors the formation of products, while a small ( K ) value indicates that reactants are favored. It helps chemists predict the concentrations of reactants and products at equilibrium and adjust reaction conditions accordingly.
