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S5 Chemistry: Rates of Reaction (Paper 2: intermediate)
S5 Chemistry: Rates of Reaction (Paper 2: intermediate)
Ten intermediate items on average rates from moles and time, tangent slope and instantaneous rate, reaction order, doubling per ten degrees, surface area and pressure effects on gaseous reactions, catalysts and equilibrium.
Direct answers Answers in order: 0.0167 mol dm-3 s-1, 8.0 cm3/s, the instantaneous rate, second order, 8 times, 2 times, same volume but faster, higher concentration, both are speeded up, and average is not instantaneous.
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: S5 Chemistry: Rates of Reaction |
| Level | S5 |
02 Questions (10 items)
- FoundationIn 300 cm3 of solution a reactant falls from 0.60 mol to zero in 2.0 minutes. What is the average rate in mol dm-3 s-1?
- Foundation0.020 mol of magnesium reacts with excess dilute hydrochloric acid and all the hydrogen is collected in 60 s. What is the average rate in cm3/s at 24 dm3/mol?
- IntermediateOn a volume against time graph, what does the tangent slope at a point represent?
- IntermediateAn experiment shows that doubling the concentration of A makes the initial rate four times larger. What order is the reaction in A?
- IntermediateThe temperature rises from 20 C to 50 C. If the rate doubles for every 10 C, by what factor does the rate change?
- ChallengeThe time needed for a reaction falls from 40 s to 20 s. By what factor does the rate change?
- ChallengeWhen 2.0 g of calcium carbonate is changed from lumps to powder with the same amount of acid, how do the final gas volume and the rate change?
- ChallengeWhy does raising the pressure of a gaseous reaction by compressing the volume speed it up?
- FoundationDoes a catalyst affect the forward and the reverse reaction in the same way?
- Error redoA student uses the average rate of the whole reaction as the instantaneous rate at one moment. What is the mistake?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 0.0167 mol dm-3 s-1 | 0.60 divided by 0.300 dm3 gives 2.0 mol dm-3, and dividing by 120 s gives 0.0167. |
| 2 | 8.0 cm3/s | 0.020 mol of hydrogen is 480 cm3, and dividing by 60 s gives 8.0 cm3/s. |
| 3 | The instantaneous rate at that moment | The tangent slope is the change over a very short time, which is the instantaneous rate. |
| 4 | Second order | The rate is proportional to the square of the concentration, so doubling gives four times, which is second order. |
| 5 | 8 times | A rise of 30 C is three intervals of 10 C, and 2 to the power 3 gives 8. |
| 6 | 2 times | With the same change, halving the time doubles the rate. |
| 7 | The final volume is the same but the rate is faster | The moles are unchanged so the volume is the same, while the larger surface area raises the rate. |
| 8 | The concentration of gas particles per unit volume rises, so collisions are more frequent | Compression raises the concentration, which increases the collision frequency and the rate. |
| 9 | Yes, it speeds up both, so the position of equilibrium is unchanged | A catalyst lowers the activation energy of both directions and only makes equilibrium arrive sooner. |
| 10 | The rate falls as the reaction proceeds, so the average rate for the whole run is not the rate at that moment | The falling concentration slows the reaction, so the average rate is usually lower than the initial rate. |
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.
For every item write the formula rate equals change divided by time first, then substitute the numbers and give the unit.Tutor Registration →
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