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Rate of Reaction Paper 1: Basics
Rate of Reaction Paper 1: Basics
Starting from the definition and units of rate, with arithmetic, the mass-loss method and the four factors that change rate.
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 1 (basics) |
02 Questions (10 items)
- FoundationMagnesium reacts with dilute hydrochloric acid and 40 cm³ of hydrogen is collected in the first 20 s. What is the average rate?
- FoundationA magnesium ribbon dissolves completely in 30 s, its mass falling from 1.2 g to zero. What is the average rate?
- FoundationA reaction consumes 0.25 mol of reactant in 5 s. What is the average rate in mol/s?
- IntermediateZinc granules react with dilute sulphuric acid and lose 12 g in 4 minutes. Give the rate in g/min and in g/s.
- IntermediateCalcium carbonate reacts with dilute hydrochloric acid and the flask with its contents loses 5.6 g in 70 s. What is the average rate?
- IntermediateEqual masses of calcium carbonate, one as powder and one as marble chips, react with acid of the same concentration. Which is faster, and is the final gas volume different?
- ChallengeIf the temperature of a reaction rises from 25 °C to 35 °C, what usually happens to the rate and why?
- ChallengeWhat does a catalyst do, and does it change the total amount of product?
- ChallengeWhich units can express a rate of reaction? Give three common forms.
- Error redoError clinic: the claim that rate equals change multiplied by time. If 80 cm³ of gas is collected in 40 s, what is the rate?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 40 divided by 20 is 2.0 cm³/s | Rate is change divided by time, and the unit must be stated; gas volumes are commonly given in cm³/s. |
| 2 | 1.2 divided by 30 is 0.04 g/s | Measuring mass loss gives a rate in grams per second, and the basis must be stated. |
| 3 | 0.25 divided by 5 is 0.05 mol/s | Moles per second is the standard chemical unit and links neatly to the equation coefficients. |
| 4 | 3.0 g/min and 0.05 g/s | Converting means multiplying minutes by sixty: 3 g/min is 1 g every 20 s, that is 0.05 g/s. |
| 5 | 5.6 divided by 70 is 0.08 g/s | The lost mass is the carbon dioxide escaping, so continuous weighing gives the rate directly. |
| 6 | the powder is faster; the final gas volume is the same because the amount of reactant is the same | Greater surface area raises the collision frequency, which changes only the rate, not the total amount that can form. |
| 7 | the rate rises noticeably, often about double, because more particles have energy above the activation energy | Heating shifts the energy distribution so a larger fraction of collisions are effective, raising the rate rather than the yield. |
| 8 | it provides a route with lower activation energy and speeds the reaction; it does not change the total product | A catalyst takes part but is regenerated, lowering the energy barrier while leaving the position of equilibrium and the yield unchanged. |
| 9 | cm³/s, g/s and mol/s, or mol per dm³ per second for concentration | The unit depends on whether volume, mass or moles are measured, and seconds alone is not a rate. |
| 10 | 80 divided by 40 is 2 cm³/s, not 3 200 cm³/s | Division, not multiplication: a larger change or a shorter time means a faster rate, so divide by 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.
Rate is always change divided by time, and the method and unit belong in the answer.Tutor Registration →
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