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Rate of Reaction Paper 2: Intermediate
Rate of Reaction Paper 2: Intermediate
Moving into data analysis: rates by interval, mass loss, syringe readings, the doubling rule for temperature, and how concentration and surface area shape the curve.
Direct answers Answers and explanations for all ten questions
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: DSE Chemistry Rate of Reaction |
| Level | Paper 2 (intermediate) |
02 Questions (10 items)
- FoundationA reaction produces 96 cm³ of gas in 40 s. What is the average rate over the first 40 s?
- FoundationIn the same experiment 60 cm³ forms in the first 20 s and another 36 cm³ in the next 20 s. Give both rates and their ratio.
- FoundationA flask and its contents fall from 100.0 g to 92.4 g in 80 s. Give the rate and say what the lost mass is.
- IntermediateA syringe collects 180 cm³ of gas in 3 minutes. What is the rate, and how long would 300 cm³ take at that rate?
- IntermediateFor a reaction whose rate doubles for every 10 °C rise, by what factor does the rate increase from 20 °C to 40 °C?
- IntermediateEqual masses of marble chips react with 1.0 M and with 0.5 M hydrochloric acid. Which is faster and why?
- ChallengeEqual masses of calcium carbonate as powder and as chips react with excess acid. How do the curves differ and how do the final volumes compare?
- ChallengeIn the thiosulphate and acid reaction the cross is obscured after 40 s at 25 °C and after 20 s at 35 °C. By what factor do the rates differ?
- ChallengeWhat happens to the rate curve and the final gas volume when a catalyst is added?
- Error redoError clinic: the claim that the rate stays the same throughout. Use the data of 60 cm³ in the first 20 s and 36 cm³ in the next 20 s to show the error.
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 96 divided by 40 is 2.4 cm³/s | An average rate uses only the start and end points and hides the change in speed between them. |
| 2 | first 3.0 cm³/s, second 1.8 cm³/s, about 1.67 times faster | The rate falls because reactant concentration decreases, so collisions become less frequent. |
| 3 | 7.6 divided by 80 is 0.095 g/s, and the loss is carbon dioxide escaping | Mass is conserved in a closed system; in an open one the loss equals the gas given off. |
| 4 | 1.0 cm³/s; 300.0 seconds | Convert minutes to seconds first; 300 divided by 1.0 gives 300 s, that is five minutes. |
| 5 | about 4 times, two doublings | Two ten-degree steps mean two doublings; such estimates hold only over a modest temperature range. |
| 6 | the 1.0 M acid; the higher concentration means more particles per unit volume and more frequent collisions | Doubling concentration raises the initial rate sharply, while the final gas volume depends on the limiting reactant. |
| 7 | the powder curve is steeper and levels off sooner; the final volumes are equal | Slope shows rate and plateau height shows total yield, and the two must be read separately. |
| 8 | about 2.0 times, since the time is halved | Compare the reciprocals of time: halving the time doubles the rate, which is more reliable than comparing seconds directly. |
| 9 | the curve is steeper and reaches the plateau sooner; the plateau height is unchanged | A catalyst changes only how fast equilibrium is reached, not where it lies, so the yield stays the same. |
| 10 | the rate falls from 3.0 to 1.8 cm³/s as reactant concentration drops, so it is not constant | Only zero-order reactions come near a constant rate; an ordinary rate curve flattens with time. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
Slope gives rate and plateau gives yield; the two must not be confused.Tutor Registration →
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