Rate of a Reaction - UNSOLVED PRACTICE SET
Chapter: Chemical Kinetics | Topic: Rate of a Reaction
RATE OF A REACTION - UNSOLVED PRACTICE SET
Topic: Rate of a Reaction
Multiple Choice Questions
1. The rate of a chemical reaction is defined as:
- Total mass of reactants consumed per unit time
- Change in concentration of reactants or products per unit time
- Volume of products formed per unit time
- Number of molecules colliding per unit time
2. For a general reaction aA + bB → cC + dD, the rate of reaction in terms of different species is related as:
- Rate = –(1/a)(d[A]/dt) = –(1/b)(d[B]/dt) = +(1/c)(d[C]/dt) = +(1/d)(d[D]/dt)
- Rate = –a(d[A]/dt) = –b(d[B]/dt) = +c(d[C]/dt) = +d(d[D]/dt)
- Rate = +(1/a)(d[A]/dt) = +(1/b)(d[B]/dt) = –(1/c)(d[C]/dt) = –(1/d)(d[D]/dt)
- Rate = a(d[A]/dt) = b(d[B]/dt) = c(d[C]/dt) = d(d[D]/dt)
3. The rate of reaction is always expressed as a:
- Positive quantity
- Negative quantity
- Zero quantity
- Variable quantity depending on the species
4. For the reaction 2H₂O₂ → 2H₂O + O₂, if the rate of disappearance of H₂O₂ is 0.30 mol L⁻¹ s⁻¹, the rate of appearance of O₂ is:
- 0.30 mol L⁻¹ s⁻¹
- 0.15 mol L⁻¹ s⁻¹
- 0.60 mol L⁻¹ s⁻¹
- 0.10 mol L⁻¹ s⁻¹
5. The instantaneous rate of a reaction is determined by:
- Drawing a tangent to the concentration-time curve at a specific point
- Calculating the average rate over a long time interval
- Measuring the total change in concentration
- Adding all rates at different time intervals
6. The units of rate of reaction are:
- mol L⁻¹
- mol L⁻¹ s⁻¹
- s⁻¹
- mol s⁻¹
Short Answer Questions
7. Distinguish between average rate and instantaneous rate of a reaction with a simple example.
8. For the reaction N₂ + 3H₂ → 2NH₃, express the rate of reaction in terms of the rate of change of concentration of each reactant and product.
9. Why is the rate of disappearance of reactants taken with a negative sign while expressing the rate of a reaction?
10. A student observes that a magnesium ribbon dissolves completely in dilute HCl in 2 minutes. Is this an example of average rate or instantaneous rate? Explain your answer.
11. For the decomposition of HI: 2HI(g) → H₂(g) + I₂(g), the rate of formation of H₂ is found to be 1.5 × 10⁻³ mol L⁻¹ s⁻¹. Calculate the rate of disappearance of HI and the rate of the overall reaction.
12. Draw a rough sketch of a concentration vs. time graph for a reactant in a chemical reaction. Label how you would determine the average rate and the instantaneous rate at time t₁.
Long Answer Questions
13. Explain the concept of rate of a chemical reaction in detail. Discuss why we need to study reaction rates and how the rate is experimentally determined using a concentration-time graph.
14. For the reaction: 2A(g) + B(g) → 3C(g) + 2D(g)
(a) Express the rate of reaction in terms of each species.
(b) If the rate of formation of C is 6.0 × 10⁻³ mol L⁻¹ s⁻¹, calculate the rate of disappearance of A, the rate of disappearance of B, and the rate of formation of D.
15. A chemistry teacher demonstrates the reaction between sodium thiosulphate and dilute HCl in the lab. The reaction is: Na₂S₂O₃ + 2HCl → 2NaCl + SO₂ + S + H₂O
(a) How can the student measure the rate of this reaction in the school laboratory?
(b) What observable change helps in determining when the reaction is complete?
Numerical / Application-Based Problems
16. For the reaction: 2N₂O₅(g) → 4NO₂(g) + O₂(g)
At a particular instant, the rate of decomposition of N₂O₅ is 1.8 × 10⁻² mol L⁻¹ s⁻¹.
(a) Calculate the rate of formation of NO₂.
(b) Calculate the rate of formation of O₂.
(c) Express the rate of the overall reaction.
17. In an experiment, the concentration of a reactant A changes from 0.50 mol L⁻¹ to 0.30 mol L⁻¹ in 20 seconds.
(a) Calculate the average rate of reaction with respect to A over this time interval.
(b) If the stoichiometry of the reaction is 2A → B, calculate the average rate of formation of B over the same time interval.
18. The following data were collected for the reaction: 2NO(g) + Cl₂(g) → 2NOCl(g)
| Time (s) | [NO] (mol L⁻¹) |
|---|---|
| 0 | 0.100 |
| 10 | 0.080 |
| 20 | 0.065 |
| 30 | 0.055 |
(a) Calculate the average rate of reaction between 0 to 10 seconds.
(b) Calculate the average rate of reaction between 10 to 20 seconds.
(c) Why does the average rate decrease as time progresses?