Rate Law and Rate Constant - UNSOLVED PRACTICE SET
Chapter: Chemical Kinetics | Topic: Rate Law and Rate Constant
RATE LAW AND RATE CONSTANT - UNSOLVED PRACTICE SET
Topic: Rate Law and Rate Constant
Multiple Choice Questions
1. The rate law for a reaction is determined by:
- The stoichiometric coefficients in the balanced equation
- Experimentally measuring the rate at different concentrations
- Theoretical calculations only
- The temperature of the reaction alone
2. For a reaction with rate law: Rate = k[A]²[B], if the concentration of A is doubled and B is kept constant, the rate becomes:
- Double
- Four times
- Half
- Unchanged
3. The rate constant (k) of a reaction depends on:
- Concentration of reactants
- Temperature and nature of the reaction
- Surface area of reactants
- Pressure of the system
4. The unit of rate constant for a reaction of order n is:
- (mol L⁻¹)^(1-n) s⁻¹
- (mol L⁻¹)^n s⁻¹
- mol L⁻¹ s⁻¹
- s⁻¹
5. If the rate law for a reaction is Rate = k[A][B]², the overall order of the reaction is:
- 1
- 2
- 3
- 0
6. The rate constant of a reaction generally increases with:
- Decrease in temperature
- Increase in temperature
- Decrease in concentration
- Addition of inert gas
Short Answer Questions
Q7. Write the rate law for the reaction: 2NO(g) + O₂(g) → 2NO₂(g), given that the reaction is second order with respect to NO and first order with respect to O₂. What is the overall order?
Q8. The rate law for a reaction is found to be Rate = k[A][B]. What will happen to the rate if:
(a) The concentration of A is tripled (B constant)?
(b) The concentrations of both A and B are doubled?
Q9. Distinguish between the rate of reaction and the rate constant of a reaction.
Q10. For a reaction with rate law Rate = k[A]^(3/2)[B]^(-1), what is the overall order of the reaction? Is this order possible? Explain.
Q11. The rate constant for a reaction at 300 K is 2.5 × 10⁻³ s⁻¹. What does this value tell you about the speed of the reaction?
Q12. Why can the rate law not be predicted from the balanced chemical equation alone? Explain with a suitable example.
Long Answer Questions
Q13. Explain how the rate law of a reaction is determined experimentally. Describe the method of initial rates with a suitable example.
Q14. (a) For the reaction: 2A + B → C + D, the following experimental data was obtained:
| Experiment | [A] (mol L⁻¹) | [B] (mol L⁻¹) | Initial Rate (mol L⁻¹ s⁻¹) |
|---|---|---|---|
| 1 | 0.10 | 0.10 | 2.0 × 10⁻³ |
| 2 | 0.20 | 0.10 | 8.0 × 10⁻³ |
| 3 | 0.20 | 0.20 | 8.0 × 10⁻³ |
Determine:
(i) The order with respect to A and B
(ii) The overall order of the reaction
(iii) The rate law
(iv) The value of the rate constant
Q15. (a) What is meant by the rate constant of a reaction? How does it differ from the rate of reaction?
(b) The rate constant of a reaction is 5.0 × 10⁻⁴ L mol⁻¹ s⁻¹ at a certain temperature. What is the order of this reaction? Justify your answer.
Numerical / Application-Based Problems
Q16. For the reaction: A + B → Products, the following data was collected:
| Experiment | [A] (mol L⁻¹) | [B] (mol L⁻¹) | Rate (mol L⁻¹ min⁻¹) |
|---|---|---|---|
| 1 | 0.10 | 0.10 | 2.0 × 10⁻³ |
| 2 | 0.20 | 0.10 | 4.0 × 10⁻³ |
| 3 | 0.10 | 0.20 | 8.0 × 10⁻³ |
(b) Write the rate law.
(c) Calculate the rate constant.
(d) Predict the rate when [A] = 0.30 mol L⁻¹ and [B] = 0.30 mol L⁻¹.
Q17. The rate law for a reaction is: Rate = k[A]²[B]
(a) If the initial rate is 0.020 mol L⁻¹ s⁻¹ when [A] = 0.10 M and [B] = 0.20 M, calculate the rate constant.
(b) What will be the new rate if [A] is increased to 0.20 M and [B] is decreased to 0.10 M?
Q18. In a school laboratory, students are studying the reaction between iodide ions and hydrogen peroxide:
2I⁻ + H₂O₂ + 2H⁺ → I₂ + 2H₂O
The rate law is found to be: Rate = k[H₂O₂][I⁻]
(a) What is the overall order of this reaction?
(b) If the concentration of H₂O₂ is doubled while keeping [I⁻] constant, by what factor does the rate increase?
(c) Does the rate depend on the concentration of H⁺ ions? What does this tell you about the mechanism?