Zero Order Reactions - UNSOLVED PRACTICE SET
Chapter: Chemical Kinetics | Topic: Zero Order Reactions
ZERO ORDER REACTIONS - UNSOLVED PRACTICE SET
Topic: Zero Order Reactions
Multiple Choice Questions
Q1. For a zero-order reaction, the rate of reaction is:
- Directly proportional to the concentration of the reactant
- Independent of the concentration of the reactant
- Inversely proportional to the concentration of the reactant
- Proportional to the square of the concentration
Q2. The integrated rate equation for a zero-order reaction is:
- k = (2.303/t) log([A]₀/[A])
- [A] = [A]₀ – kt
- 1/[A] = 1/[A]₀ + kt
- [A] = [A]₀e^(-kt)
Q3. The unit of rate constant for a zero-order reaction is:
- s⁻¹
- mol L⁻¹ s⁻¹
- L mol⁻¹ s⁻¹
- L² mol⁻² s⁻¹
Q4. For a zero-order reaction, a graph of [A] vs. time gives:
- A straight line passing through the origin
- A straight line with a negative slope and intercept [A]₀
- A curve
- A straight line with a positive slope
Q5. The half-life of a zero-order reaction is:
- Independent of initial concentration
- Directly proportional to initial concentration
- Inversely proportional to initial concentration
- Independent of the rate constant
Q6. An example of a zero-order reaction is:
- Decomposition of HI on a gold surface
- Radioactive decay
- Hydrolysis of ethyl acetate
- Decomposition of N₂O₅
Short Answer Questions
Q7. Write the rate law and integrated rate equation for a zero-order reaction. What is the unit of its rate constant?
Q8. For a zero-order reaction, derive the expression for half-life (t₁/₂) in terms of initial concentration [A]₀ and rate constant k.
Q9. Why does the half-life of a zero-order reaction decrease as the reaction progresses?
Q10. Draw a rough sketch of [A] vs. time for a zero-order reaction. Label the slope, intercept, and half-life on the graph.
Q11. The decomposition of NH₃ on a platinum surface is a zero-order reaction. Explain why the rate does not depend on the concentration of NH₃.
Q12. For a zero-order reaction, the concentration of reactant decreases from 0.50 M to 0.30 M in 20 minutes. Calculate the rate constant.
Long Answer Questions
Q13. Derive the integrated rate equation for a zero-order reaction: A → Products. Show that a plot of [A] vs. time is a straight line and explain how the rate constant can be determined from this graph.
Q14. (a) What are the characteristics of a zero-order reaction? List at least four.
(b) The decomposition of N₂O on a hot platinum surface is a zero-order reaction. Explain why this happens and write the rate law for this reaction.
Q15. (a) For a zero-order reaction, show mathematically that t₁/₂ = [A]₀ / 2k.
(b) If the initial concentration of a reactant in a zero-order reaction is 0.80 M and the rate constant is 4.0 × 10⁻² mol L⁻¹ min⁻¹, calculate:
(i) The half-life of the reaction
(ii) The time required for the concentration to drop to 0.20 M
(iii) The concentration after 30 minutes
Numerical / Application-Based Problems
Q16. For a zero-order reaction: A → Products, the rate constant is 2.0 × 10⁻² mol L⁻¹ s⁻¹. The initial concentration of A is 1.0 mol L⁻¹.
(a) Write the integrated rate equation.
(b) Calculate the concentration of A after 20 seconds.
(c) Calculate the time required for the reaction to be 80% complete.
(d) Calculate the half-life of the reaction.
Q17. The following data were obtained for a zero-order reaction:
| Time (s) | [A] (mol L⁻¹) |
|---|---|
| 0 | 0.80 |
| 10 | 0.60 |
| 20 | 0.40 |
| 30 | 0.20 |
(a) Verify that this is a zero-order reaction by calculating the rate constant at different time intervals.
(b) Determine the rate constant from the graph (conceptually, describe how).
(c) Predict the concentration of A at t = 40 s.
(d) Calculate the half-life from the beginning and from t = 10 s. Are they the same? Explain.
Q18. In a photochemical reaction involving H₂ and Cl₂, the rate of formation of HCl is found to be independent of the concentration of Cl₂ as long as light is present. This suggests zero-order behavior with respect to Cl₂.
(a) Write the rate law for this reaction with respect to Cl₂.
(b) Explain why the rate is independent of [Cl₂] in the presence of light.
(c) If the rate constant is 1.5 × 10⁻³ mol L⁻¹ s⁻¹ and the initial [Cl₂] is 0.50 M, calculate how long it will take for the concentration of Cl₂ to drop to 0.10 M. (Assume zero order with respect to Cl₂.)