Ten original SPM-style multiple-choice questions with answers and one-line reasons, plus three structured questions with model answers, covering rate, the four factors, collision theory, catalysts and graphs for the Form 4 Rate of Reaction chapter.
Use these original questions for timed practice, then check each answer and the short reason against your own working. They are written in SPM style on the Form 4 Rate of Reaction standards; they are not past-year papers. Cover the answers first.
Paper-1-style multiple-choice questions
1. Which unit is suitable for the rate of a reaction that produces a gas? A. cm³ B. cm³ s⁻¹ C. s D. g Answer: B. Rate is a quantity per unit time, so a volume divided by time gives cm³ s⁻¹.
2. Magnesium reacts with dilute hydrochloric acid. Which change will not increase the rate? A. Warming the acid B. Using more concentrated acid C. Using larger lumps of magnesium instead of powder D. Adding a suitable catalyst Answer: C. Larger lumps have a smaller total surface area, which lowers the rate.
3. In collision theory, an effective collision is one in which the particles have A. any energy and any direction B. energy ≥ activation energy and the correct orientation C. the correct orientation only D. energy below the activation energy Answer: B. Both the energy condition and the orientation condition must be met.
4. A catalyst increases the rate of reaction because it A. raises the activation energy B. provides an alternative path with a lower activation energy C. increases the temperature D. increases the concentration of reactants Answer: B. The alternative path makes a larger fraction of collisions effective.
5. On a graph of volume of gas against time, the rate of reaction is greatest A. at the plateau B. at the very start C. near the end D. it is constant throughout Answer: B. The gradient is steepest at the start, when the reactant concentration is highest.
6. In the reaction of sodium thiosulfate with acid, the mark under the flask disappears in 50 s at one temperature and 25 s at a higher temperature. Compared with the first, the rate at the higher temperature has A. halved B. doubled C. stayed the same D. become four times smaller Answer: B. Rate ∝ 1 ÷ time, and the time has halved, so the rate has doubled.
7. Which factor changes the rate of a gas-phase reaction but has no effect on a reaction between solids and a solution? A. Temperature B. Pressure C. Catalyst D. Concentration Answer: B. Pressure changes the rate only when gases are involved.
8. Equal masses of marble chips and marble powder react with excess dilute acid. Which quantity is the same for both? A. The initial rate B. The time to finish C. The final volume of carbon dioxide D. The steepness of the curve at the start Answer: C. The same mass of marble releases the same amount of gas; only the speed differs.
9. Which statement about a catalyst is correct? A. Its mass decreases during the reaction B. It is chemically unchanged at the end C. It becomes one of the products D. It increases the yield of product Answer: B. A catalyst is recovered chemically unchanged and can be reused.
10. A reaction releases 48 cm³ of gas in 24 s. The average rate over this time is A. 0.5 cm³ s⁻¹ B. 2 cm³ s⁻¹ C. 24 cm³ s⁻¹ D. 1152 cm³ s⁻¹ Answer: B. Average rate = 48 cm³ ÷ 24 s = 2 cm³ s⁻¹.
Structured questions
Structured 1, Concentration and collision theory. A student reacts excess zinc granules with 25 cm³ of dilute hydrochloric acid and measures the volume of hydrogen collected every 30 s. The experiment is repeated with a more concentrated acid, everything else kept the same.
(a) State the manipulated and responding variables. (b) Explain, using collision theory, why the more concentrated acid gives a faster rate. (c) Sketch and describe how the two curves compare.
Model answer. (a) The manipulated variable is the concentration of the acid; the responding variable is the volume of hydrogen collected (per unit time). (b) In the more concentrated acid there are more acid particles in the same volume, so the particles collide more frequently; the frequency of effective collisions increases, so the rate increases. (c) The curve for the more concentrated acid rises more steeply at the start (higher initial rate). Because the zinc is in excess and the amount of acid decides the hydrogen produced, the more concentrated acid also reaches a higher final volume; both curves then level off.
Structured 2, Catalysts. Hydrogen peroxide decomposes slowly to water and oxygen. When manganese(IV) oxide is added, oxygen is released rapidly.
(a) Define a catalyst. (b) Explain, in terms of activation energy, how the manganese(IV) oxide speeds up the reaction. (c) State one way to show that the manganese(IV) oxide is chemically unchanged.
Model answer. (a) A catalyst is a substance that alters the rate of a chemical reaction while remaining chemically unchanged at the end. (b) It provides an alternative reaction path with a lower activation energy, so a larger fraction of collisions now have enough energy to be effective; the frequency of effective collisions rises and the rate increases. (c) Filter, wash, dry and reweigh the manganese(IV) oxide at the end; its mass is unchanged, showing it was not used up.
Structured 3, Reading a rate graph. In a reaction between a metal carbonate and dilute acid, the total volume of carbon dioxide is recorded against time. The curve rises and reaches a plateau at 72 cm³ after 90 s; it passes through 48 cm³ at 30 s.
(a) Calculate the average rate over the first 30 s. (b) State and explain how the rate at 60 s compares with the rate at 10 s. (c) State what the plateau tells you about the reaction.
Model answer. (a) Average rate = 48 cm³ ÷ 30 s = 1.6 cm³ s⁻¹. (b) The rate at 60 s is lower than at 10 s, because the acid has been partly used up, so its concentration is lower and effective collisions are less frequent, the gradient is gentler. (c) The plateau at 72 cm³ shows the reaction has stopped: the limiting reactant has been completely used up, so no more gas is produced.
After you finish
Mark yourself strictly. For every explanation, check that you reached “frequency of effective collisions” and, for every graph answer, that you separated the gradient (rate) from the plateau (amount). If two or three questions expose the same slip, revisit that content standard in the revision notes and try the worked examples again. A one-to-one teacher can set you a fresh mix at the right level and mark your collision-theory chains line by line, which is where SPM Chemistry marks are won in this chapter.
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