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S5 Chemistry Rates of Reaction, Paper 3: measuring instruments, order of reaction and rate ratios
S5 Chemistry Rates of Reaction, Paper 3: measuring instruments, order of reaction and rate ratios
Ten graded items from colorimetry and catalyst routes through two-stage rates and temperature steps to rate ratios, each with an answer.
Focus Powder changes speed, not yield; work out each stage before dividing; count the ten-degree steps; heating works through kinetic energy.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 25 |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S5 Chemistry: Rates of Reaction |
| Level | Four basic, three advanced, two challenge and one error-repair item |
02 Questions (10 items)
- Foundation72 cm^3 of carbon dioxide is collected in 60 s. What is the average rate?
- FoundationWhy does a catalyst speed a reaction up?
- FoundationSame mass of marble, powder instead of one lump: how does the total carbon dioxide compare?
- FoundationWhich instrument best follows a reaction whose solution fades from dark to pale?
- IntermediateA concentration falls from 0.50 to 0.40 in the first 10 s and to 0.34 in the next 10 s. Find the ratio of the two average rates.
- IntermediateIf the rate is proportional to the square of the concentration, how does it change when the concentration rises from 0.10 to 0.30 mol dm^-3?
- IntermediateIf the rate doubles for every 10 C rise, how many times faster is the reaction at 50 C than at 20 C?
- Challenge1.20 mol of reactant falls to 0.45 mol in 25 s. Find the average rate in mol s^-1.
- ChallengeRun A gives 90 cm^3 in 45 s and run B gives 60 cm^3 in 40 s. How many times faster is A?
- Error redoError repair: a student says heating speeds a reaction because the particles expand and hit each other over a larger area. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 1.2 cm^3 s^-1 | Rate is volume over time, so 72 divided by 60 gives 1.2. |
| 2 | It provides an alternative route of lower activation energy | A catalyst offers a different route with a lower activation energy, so more collisions are successful. |
| 3 | The same, but the powder gives it faster | The total depends only on the number of moles; powder just has a bigger surface area and reacts faster. |
| 4 | A colorimeter | A colorimeter measures absorbance, turning the depth of colour into a number that can be read at fixed times. |
| 5 | About 1.67 : 1 | The first ten seconds give 0.010 and the next 0.006 mol dm^-3 s^-1, so the ratio is 1.67. |
| 6 | Nine times faster | The concentration triples and squaring that gives nine times the rate. |
| 7 | Eight times | A rise of 30 C is three ten-degree steps, and two cubed is eight. |
| 8 | 0.030 mol s^-1 | 0.75 mol is used up, which divides by 25 s to give 0.030. |
| 9 | About 1.33 times | Run A gives 2.0 and run B 1.5 cm^3 per second, so A is about 1.33 times faster. |
| 10 | Particles do not expand; heating raises kinetic energy and the fraction of successful collisions | Heating raises the average kinetic energy, so a larger fraction of collisions exceed the activation energy. |
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.
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Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.
