How should units of rate be handled?

Rate is change divided by time, so use cm^3 s^-1 for gas volume and mol s^-1 for moles.

How do I count ten-degree steps?

From 20 C to 50 C is three steps of 10 C, so the rate multiplies by two three times.

S5 Chemistry Rates of Reaction, Paper 1: average rate, temperature and catalysts

2026-11-02

Ten graded items from gas volume rates through temperature effects and surface area to tangent gradients, each with an answer.

Focus　Rate is always change over time; count the ten-degree steps carefully; a catalyst changes speed, not yield.

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)

Foundation60 cm^3 of gas is collected in 30 s. What is the average rate?
FoundationWith all else unchanged, doubling the acid concentration makes the rate about how many times larger?
FoundationHow does a catalyst speed up a reaction?
FoundationWhy does powdering marble speed up its reaction with acid?
IntermediateIf the rate doubles for every 10 C rise, how many times faster is the reaction at 50 C than at 20 C?
IntermediateOne run releases 100 cm^3 in 40 s and another takes 80 s. What is the ratio of their average rates?
IntermediateWhy does the rate fall as a reaction proceeds?
Challenge0.80 mol of reactant falls to 0.40 mol in 30 s. Find the average rate in mol s^-1 over that period.
ChallengeA concentration-time graph has a tangent gradient of 1.6 cm^3 s^-1 at t = 0 and 0.40 cm^3 s^-1 at 60 s. How many times faster is the initial rate?
Error redoError repair: a student claims a catalyst raises the total yield. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	2.0 cm^3 s^-1	Rate is volume divided by time, so 60 divided by 30 gives 2.0.
2	About twice	Doubling the concentration doubles the collision frequency, so the rate roughly doubles.
3	It provides an alternative pathway of lower activation energy	A catalyst lowers the activation energy so more particles have enough energy to react.
4	The surface area increases, giving more collisions	Powder exposes far more surface area, so more particles meet the acid.
5	Eight times	A rise of 30 C is three ten-degree steps, so the rate multiplies by two three times, giving eight.
6	2 : 1	The rates are 2.5 and 1.25 cm^3 per second, so the ratio is two to one.
7	The reactant concentration falls, so collisions become less frequent	Reactants are used up, so collisions become less frequent and the rate falls.
8	0.0133 mol s^-1	0.40 mol is used up, which divides by 30 s to give 0.0133 mol per second.
9	Four times	The tangent gradient is the instantaneous rate, and 1.6 divided by 0.40 gives four.
10	A catalyst speeds up the reaction but does not change the yield	A catalyst only shortens the time to reach equilibrium; the position and the yield stay the same.

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.