Guided lesson

Measuring Rates

4CH1-3.104CH1-3.9

3 guided lessons · 27 checks · 3. Physical Chemistry → Rates of Reaction

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Lesson 1 of 3

Experiments on surface area and concentration

Two experiments anchor the surface area and concentration stories: marble chips fizzing in acid, and a cloudy cross disappearing under thiosulfate. This lesson walks both methods and the measurements each one collects.

What you know already

From Energetics you already know how to follow a reaction with a thermometer. This note follows it with a stopwatch instead, describing the experiments that test how surface area, concentration, temperature and catalysts change the pace of a reaction. It closes by reading the same story off rate graphs.

Key points of understanding

The surface area experiment adds marble chips to dilute hydrochloric acid and collects the gas produced.
A delivery tube feeds the gas into an inverted measuring cylinder in a water trough.
Gas volume over a fixed time is measured, then the run repeats with different chip sizes.
The concentration experiment watches a cross under the flask disappear as the mixture clouds.
Sodium thiosulfate is diluted with water to give different concentrations for each repeat.

Effect of Surface Area on a Reaction Rate

Investigating effect of concentration on rate reaction — The apparatus needed to investigate the effect of concentration on the rate of reaction

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1.Experiments on surface area and concentration

4CH1-3.9

Key points

The surface area experiment adds marble chips to dilute hydrochloric acid and collects the gas produced.
A delivery tube feeds the gas into an inverted measuring cylinder in a water trough.
Gas volume over a fixed time is measured, then the run repeats with different chip sizes.
The concentration experiment watches a cross under the flask disappear as the mixture clouds.
Sodium thiosulfate is diluted with water to give different concentrations for each repeat.

First pass

Bigger chips or stronger acid should change how fast gas bubbles appear or how quickly a cross vanishes under cloudy liquid. Each experiment changes one factor, times the result and repeats with a new size or strength.

Analogy — It is like timing how fast sugar vanishes in stirred tea: one lump versus crushed sugar, or weak tea versus strong.

Exam pointer — Name the measured quantity, gas volume or disappearance time, and the factor varied in each method.

Going deeper

For surface area, marble chips react with dilute hydrochloric acid and the gas collected in a fixed time is compared across chip sizes. For concentration, sodium thiosulfate of different strengths reacts with acid while a stopwatch times how long a marked cross stays visible through the clouding mixture.

Analogy — The first is a race of bubbling, the second a race of fading; both stop the clock the moment a fixed landmark is reached.

Exam pointer — Describe apparatus and timing for both methods, and state how the factor is varied between repeats.

Checks

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1.What is measured in the marble chip experiment?
2.Why is the measuring cylinder inverted in a water trough?
3.How are different concentrations of sodium thiosulfate prepared?
4.When does the stopwatch stop in the concentration experiment?
5.Increasing the concentration of the thiosulfate has what effect on the result?
6.State where the gas is collected in the surface area experiment.
Written response · recall
Your answer
7.State what is watched in the concentration experiment as the mixture clouds.
Written response · recall
Your answer
8.Explain why sodium thiosulfate is diluted with water in the concentration experiment.
Written response · explain why
Your answer
9.Two chip sizes are tested and the gas volume read after the same fixed time. State the comparison this timing choice allows.
Written response · application
Your answer

2.Experiments on temperature and catalysts

4CH1-3.9

Two more experiments complete the set: magnesium in warmed acid, and hydrogen peroxide breaking down with and without a black powder. This lesson times both and explains what each comparison proves.

Investigating the effect of temperature on rate of reaction — Diagram showing the apparatus needed to investigate the effect of temperature on the rate of reaction

Investigating effect of catalyst on rate reaction — Diagram showing the apparatus needed to investigate the effect of a catalyst on the rate of reaction

Key points

The temperature experiment heats dilute hydrochloric acid to a set temperature in a water bath.
A strip of magnesium is added, the stopwatch started, and the time taken for the metal to dissolve is recorded.
The experiment is repeated at different temperatures and the results compared.
The catalyst experiment adds manganese(IV) oxide to hydrogen peroxide and collects the oxygen produced.
The run is repeated without the catalyst so the two gas volumes can be compared.

First pass

Warm the acid to a chosen temperature, drop in magnesium and time how long it takes to vanish; then try a hotter bath. For catalysts, run the peroxide reaction with the powder and again without, and compare the gas collected.

Analogy — One test is timing how fast sugar dissolves in warm versus cool tea; the other is checking whether a pinch of powder makes a bottle fizz faster.

Exam pointer — State the timed quantity and the comparison run for each experiment, with the factor varied named.

Going deeper

Dilute hydrochloric acid is warmed to a set temperature in a water bath, magnesium is added, and the time for the metal to fully dissolve is recorded before repeating at other temperatures. In the catalyst experiment the oxygen collected from hydrogen peroxide in a fixed time is compared with and without manganese(IV) oxide.

Analogy — The magnesium race gets faster as the water bath climbs, while the peroxide test is a race run twice, once with a helper and once without.

Exam pointer — Quote the water bath, the dissolve time and the with-and-without comparison when describing these methods.

Checks

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1.What times the end of the temperature experiment?
2.Why does the acid sit in a water bath before the magnesium is added?
3.In the catalyst experiment, what is collected in the inverted measuring cylinder?
4.Why run the peroxide experiment a second time without the catalyst?
5.Which factor is deliberately changed between the two peroxide runs?
6.State what is measured in the temperature experiment once the magnesium strip is added.
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Your answer
7.State the catalyst added to hydrogen peroxide in the catalyst experiment.
Written response · recall
Your answer
8.Explain why the catalyst experiment is repeated without the catalyst.
Written response · explain why
Your answer
9.A student heats the acid to 40 degrees Celsius for one run and 60 degrees Celsius for another. State which piece of apparatus keeps each run at its set temperature.
Written response · application
Your answer

3.Factors, graphs and the economic angle

4CH1-3.10

Four factors govern how fast reactions run, and each leaves a fingerprint on the rate graph. This lesson collects the fingerprints and adds the industrial reason anyone cares.

Key points

The factors affecting rate are concentration or pressure, temperature, surface area of solids and catalysts.
A faster reaction shows a steeper starting gradient that becomes horizontal sooner.
Graphs for changed conditions still finish at the same amount of product.
Increasing the concentration, pressure, temperature or surface area each increases the rate of reaction.
Industry favours higher rates because faster production is more efficient and sustainable.

First pass

Every factor that packs particles closer or makes them livelier steepens the start of the graph. The curve flattens at the same final product amount, and industry chases that steep start for cheaper production.

Analogy — It is like three routes up the same hill: steeper starts reach the top sooner, but the summit height never changes.

Exam pointer — Sketch or describe the steeper-start-same-plateau shape and name the four rate factors.

Going deeper

Compared with the slower condition, a faster reaction line starts with a steeper gradient and flattens sooner while forming the same amount of product. Concentration, pressure, temperature, surface area and catalysts are the levers, and raising the first four raises the rate that industry prizes.

Analogy — Two commuters reach the same office, but the express train gets there earlier and waits; the destination is fixed, only the pace differs.

Exam pointer — Compare two lines by gradient, plateau timing and final product, and tie faster rates to production efficiency.

Checks

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1.What shape distinguishes the graph of a faster reaction from a slower one?
2.Two reactions differ only in temperature. What is true of their final product amounts?
3.Which list names all four factors that can affect the rate of a reaction?
4.Why are faster rates of industrial interest?
5.Powdering a solid reactant instead of using one lump does what to the rate graph?
6.State the four factors affecting the rate of a reaction.
Written response · recall
Your answer
7.State how a faster reaction looks different on a rate graph.
Written response · recall
Your answer
8.Explain why graphs for reactions run under changed conditions all finish at the same amount of product.
Written response · explain why
Your answer
9.A chemical plant wants to make its product faster without hiring more staff. State the commercial benefit of raising the rate of reaction.
Written response · application
Your answer

From the revision note

Diagrams on this note's page that are not tied to a specific lesson.

How pressure and concentration affect the rate of reaction — Increasing the concentration of a solution or gas pressure increases the rate of reaction

How temperature affects the rate of reaction — Increasing the temperature increases the rate of reaction

How surface area affects the rate of reaction — Increasing the surface area increases the rate of reaction

Surface Area of a Solid Reactant, IGCSE & GCSE Chemistry revision notes

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1.Experiments on surface area and concentration

4CH1-3.9

2.Experiments on temperature and catalysts

4CH1-3.9

Two more experiments complete the set: magnesium in warmed acid, and hydrogen peroxide breaking down with and without a black powder. This lesson times both and explains what each comparison proves.