Describe — 4 marks
A student investigates how temperature affects the rate of reaction between hydrochloric acid and calcium carbonate powder. The student measures the time taken for the reaction to produce 50 cm³ of carbon dioxide gas at different temperatures.
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(a) Describe what happens to the rate of reaction as the temperature increases from 20 °C to 60 °C.
[2 marks]
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(b) Describe, in terms of particle collisions, why increasing the temperature causes the rate of reaction to increase.
[2 marks]
Show mark scheme
- (a) The rate of reaction increases / the time taken decreases (1 mark)
- (a) As temperature increases, the reaction happens faster / carbon dioxide is produced more quickly (1 mark)
- (b) Increasing temperature gives particles more kinetic energy / particles move faster (1 mark)
- (b) This causes more frequent collisions between reactant particles and/or collisions occur with greater energy / particles are more likely to collide with sufficient energy to react (1 mark)
Calculate — 5 marks
A student investigates how the rate of reaction changes when calcium carbonate powder reacts with dilute hydrochloric acid. The student measures the volume of gas produced at regular time intervals. The results are shown in the table below:
Time (s) | 0 | 10 | 20 | 30 | 40 | 50
Volume of CO₂ (cm³) | 0 | 45 | 80 | 105 | 120 | 120
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(a) Calculate the rate of reaction between 0 and 10 seconds, in cm³/s.
[2 marks]
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(b) Calculate the rate of reaction between 20 and 40 seconds, in cm³/s.
[2 marks]
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(c) Explain why the rate of reaction changes between these two time periods.
[1 mark]
Show mark scheme
- (a) Change in volume = 45 - 0 = 45 cm³ (1 mark)
- (a) Rate = 45 ÷ 10 = 4.5 cm³/s (1 mark)
- (b) Change in volume = 120 - 80 = 40 cm³ (1 mark)
- (b) Rate = 40 ÷ 20 = 2.0 cm³/s (1 mark)
- (c) The rate decreases because the concentration of hydrochloric acid decreases as it is used up in the reaction / particles have fewer collisions (1 mark)
Show — 4 marks
A student investigates how temperature affects the rate of reaction between calcium carbonate powder and dilute hydrochloric acid. The student measures the volume of gas produced at different temperatures and records the results in a table.
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(a) The student carried out the reaction at 20°C and collected 60 cm³ of gas in 120 seconds. Show that the rate of reaction at 20°C is 0.5 cm³/s.
[1 mark]
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(b) At 40°C, the student collected 60 cm³ of gas in 60 seconds. Calculate the rate of reaction at 40°C.
[1 mark]
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(c) Show how the rate of reaction changed when the temperature increased from 20°C to 40°C. Use your answers from parts (a) and (b) to explain your answer.
[2 marks]
Show mark scheme
- (a) Correct calculation: 60 ÷ 120 = 0.5 cm³/s (or equivalent working shown)
- (b) Correct calculation: 60 ÷ 60 = 1 cm³/s (or equivalent working shown)
- (c) The rate of reaction increased / doubled (1 mark)
- (c) When temperature increased from 20°C to 40°C, the rate increased from 0.5 cm³/s to 1 cm³/s, showing that higher temperature increases the rate of reaction (1 mark)
Explain — 3 marks
A student investigates the rate of reaction between sodium thiosulfate solution and dilute hydrochloric acid. The reaction produces a cloudy precipitate of sulfur. The student places the flask over a cross drawn on paper and records how long it takes for the cross to disappear. The student repeats the experiment using sodium thiosulfate solution at a higher temperature.
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(a) State what happens to the time taken for the cross to disappear when the temperature of the sodium thiosulfate solution is increased.
[1 mark]
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(b) Explain why increasing the temperature increases the rate of reaction.
[2 marks]
Show mark scheme
- (a) time taken decreases / reaction is faster / cross disappears quicker
- (b) particles gain more kinetic energy / move faster
- (b) more frequent collisions (per second) / more successful collisions per unit time
Describe — 2 marks
A student investigates the reaction between calcium carbonate chips and dilute hydrochloric acid. The reaction produces carbon dioxide gas. The student wants to compare how quickly the reaction happens using large chips compared to powdered calcium carbonate.
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(a) Describe one observation the student would make during this reaction.
[1 mark]
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(b) Describe how the student could measure the rate of this reaction.
[1 mark]
Show mark scheme
- (a) bubbles / fizzing / effervescence (seen)
- (a) solid dissolves / gets smaller
- (a) cloudy/milky (if limewater mentioned in context)
- (b) measure volume of gas produced per unit time
- (b) measure mass lost per unit time
- (b) time how long to produce a fixed volume of gas
- (b) time how long for solid to disappear
GCSE Perfect