GCSE Chemistry Rates questions by topic

Name a method to measure the rate of each reaction.

1. (a)Magnesium ribbon reacting with acid, making hydrogen[1]
2. (b)Sodium thiosulfate reacting with acid, making a cloudy precipitate[1]
3. (c)Any reaction making a gas, as an alternative to (a)[1]

A reaction produces 45 cm³ of gas in 30 seconds.

1. (a)Calculate the mean rate in cm³/s.[1]
2. (b)State what would happen to the rate as the reactants get used up.[1]

Explain why food keeps longer in a fridge.

1. (a)State the effect of lower temperature on the rate of spoilage reactions.[1]
2. (b)Explain the effect using collision theory.[2]

Copy and complete: A catalyst is a substance that … the rate of a reaction without being … It works by lowering the …

1. (a)First blank[1]
2. (b)Second blank[1]
3. (c)Third blank[1]

A student times how long a cross takes to disappear for four acid concentrations.

1. (a)Describe the trend in the results.[2]
2. (b)Explain the trend using collision theory.[3]

Complete the table of mean rates for gas-producing reactions.

1. (a)Calculate the missing rate in row 1.[1]
2. (b)Calculate the missing time in row 2.[1]
3. (c)Calculate the missing volume in row 3.[1]
4. (d)Calculate the missing time in row 4.[1]
5. (e)State the equation linking mean rate, volume and time.[1]

Complete the sentences about collision theory, then apply them.

1. (a)Reactions happen only when particles collide with at least the … energy.[1]
2. (b)A higher temperature makes particles move …, so collisions are more … and more of them are successful.[1]
3. (c)Crushing a solid into powder increases its surface …, so more particles are … to react.[1]
4. (d)A student warms dilute acid before adding magnesium. Explain the effect on the rate.[1]
5. (e)State one way to slow the reaction in (d) without changing the concentration.[1]

Explain each observation using collision theory.

1. (a)Food cooks faster in a pressure cooker.[2]
2. (b)A fire burns fiercer in oxygen than in air.[2]
3. (c)Crushed ice dissolves faster in water than one large ice cube.[2]

The disappearing-cross practical is repeated by a different student who obtains systematically longer times.

1. (a)Suggest two reasons the times differ between students.[2]
2. (b)Describe one improvement using a sensor.[2]
3. (c)State why repeats are taken.[1]

Hydrogen peroxide decomposes slowly; with manganese(IV) oxide it fizzes vigorously, and 1.20 g of black solid remains at the end.

1. (a)Name the role of the black solid.[1]
2. (b)The original mass added was 1.20 g. What does this show?[2]
3. (c)Explain how the solid speeds the reaction.[2]
4. (d)Name the gas collected and its test.[1]

Two gas-syringe experiments use the same marble mass with acid of concentrations 1.0 and 2.0 mol/dm³.

1. (a)Sketch or describe how the two volume–time curves compare.[3]
2. (b)Explain the comparison using collision theory.[3]

Marble chips react with hydrochloric acid in a sealed flask attached to a gas syringe. The syringe readings are 0 cm³ at 0 s, 42 cm³ at 20 s and 70 cm³ at 40 s.

1. (a)Calculate the mean rate of gas production over the first 40 s.[2]
2. (b)A tangent drawn at 20 s rises from 30 cm³ at 10 s to 60 cm³ at 30 s. Calculate the rate at 20 s.[2]
3. (c)Explain why the rate at 20 s is higher than the mean rate over the whole 40 s.[2]

Hydrogen peroxide decomposes to give oxygen. With no catalyst it releases 8 cm³ in the first 60 s; with 0.5 g of manganese(IV) oxide powder it releases 8 cm³ in the first 6 s. Both runs eventually reach 24 cm³.

1. (a)Calculate the mean rate over the first 8 cm³ for each run.[2]
2. (b)State how many times faster the catalysed run is, over this stage.[1]
3. (c)Explain how the catalyst speeds the reaction.[2]
4. (d)State what should be true of the catalyst’s mass at the end, and why this matters for the comparison.[1]

From a volume–time curve, a tangent at 50 s rises from 20 cm³ to 56 cm³ between 40 s and 60 s.

1. (a)Calculate the rate at 50 s.[2]
2. (b)Explain why the tangent method is needed rather than dividing total volume by total time.[2]
3. (c)The mean rate over the whole reaction (0–120 s) is 0.5 cm³/s. State the total volume collected.[2]
4. (d)Compare the rate at 50 s with the mean rate.[1]

Design an investigation into how temperature affects the rate of magnesium and hydrochloric acid.

1. (a)State the independent and dependent variables.[2]
2. (b)List three control variables and why each matters.[3]
3. (c)Describe how the rate would be measured.[2]
4. (d)State one safety precaution.[1]

A student argues: “Powders react faster than lumps because powder particles have more energy.”

1. (a)Identify the error in the student’s statement.[2]
2. (b)Write the correct explanation.[3]
3. (c)State one experiment that would test the student’s claim fairly.[1]

Magnesium reacts with excess dilute sulfuric acid in a gas syringe. The readings are: 0 cm³ at 0 s, 32 cm³ at 10 s, 52 cm³ at 20 s, 64 cm³ at 30 s, 70 cm³ at 40 s, 72 cm³ at 50 s and 72 cm³ at 60 s.

1. (a)Calculate the mean rate of gas production during the first 20 seconds.[2]
2. (b)A tangent at 10 s passes through 14 cm³ at 5 s and 48 cm³ at 15 s. Calculate the rate at 10 s.[2]
3. (c)Explain why the curve levels off after 40 s.[1]
4. (d)Predict and explain the effect of repeating the experiment 10 °C warmer on the shape of the curve.[2]

Two students compare acid concentrations using the disappearing-cross method with 0.10 g of magnesium powder. Student A used 1.0 mol/dm³ acid and a mean vanish time of 45 s; student B used 2.0 mol/dm³ acid, a mean vanish time of 20 s, but poured 50 cm³ of acid where student A used 25 cm³. Neither recorded the room temperature.

1. (a)Calculate a rate value (1 ÷ time) for each student.[2]
2. (b)State which student’s reaction was faster and identify the variable responsible.[2]
3. (c)Identify two ways the comparison is unfair or unreliable, and give a fix for each.[3]
4. (d)Predict how the volume–time curve for student B would compare with student A’s.[1]