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GCSE · Chemistry

IG.C10 Rates of Reaction: Collision Theory and Measuring Rate

EDEXCEL 4CH1 · Calculator allowed · about 60 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

State, in the context of collision theory, the two main requirements for reactant particles to react when they collide in a gas or solution.

(Total for Question 1 is 1 mark)

Describe how increasing the concentration of a reactant in solution affects the rate of reaction, using collision theory to explain the change.

(Total for Question 2 is 2 marks)

Explain how increasing the temperature from 20 degrees C to 50 degrees C increases reaction rate in terms of both collision frequency and collision energy.

(Total for Question 3 is 2 marks)

A student investigates the reaction of marble chips (calcium carbonate) with dilute hydrochloric acid and measures the loss of mass every 30 seconds using a balance. Describe two control variables the student should keep constant to make the test fair, and explain why each must be controlled.

(Total for Question 4 is 3 marks)

Sketch and describe the expected shape of a graph showing mass of flask plus contents against time for the marble chips and dilute acid experiment, starting at time zero when acid is added.

(Total for Question 5 is 3 marks)

A reaction is monitored by collecting gas in a gas syringe. The student records volume of gas every 10 seconds. Give one practical advantage of using a gas syringe compared with measuring loss of mass on a balance for a gas-producing reaction.

(Total for Question 6 is 2 marks)

In the disappearing cross experiment, sodium thiosulfate reacts with hydrochloric acid to produce a cloudy mixture. Explain how the time taken for the cross to disappear depends on particle collisions, and suggest one way to make the reaction faster.

(Total for Question 7 is 3 marks)

A student measures the volume of hydrogen gas produced when 0.50 g magnesium reacts with excess dilute hydrochloric acid. The readings are: 0 s: 0.0 cm3, 10 s: 12.0 cm3, 20 s: 20.0 cm3, 30 s: 24.0 cm3. Calculate the mean rate of gas production between 10 s and 30 s in cm3 per second. Show working.

(Total for Question 8 is 3 marks)

Data from a loss of mass experiment are: time 0 s: mass 52.00 g; 30 s: 51.60 g; 60 s: 51.35 g. Calculate the mean rate of mass loss between 0 s and 60 s in grams per second. Show working and give answer to 3 significant figures.

(Total for Question 9 is 3 marks)

A student records the volume of gas produced every 15 seconds and plots a volume-time graph. Explain how the initial rate of reaction is determined from the graph and what it represents physically.

(Total for Question 10 is 2 marks)

A student repeats the reaction of sodium thiosulfate and hydrochloric acid three times at the same concentration and records times for the cross to disappear: 32.0 s, 28.5 s, 30.5 s. Calculate the mean time and state one simple reason for repeating measurements.

(Total for Question 11 is 4 marks)

Explain how a catalyst increases the rate of a reaction, using collision theory language but do not draw an energy profile diagram.

(Total for Question 12 is 4 marks)

Predict qualitatively how reducing the particle size of a solid reactant, while keeping its mass constant, will change the initial rate measured by loss of mass in the marble chips experiment, and explain why.

(Total for Question 13 is 2 marks)

A student measures gas volume from a reaction and obtains a straight-line section on the volume-time graph between 40 s and 70 s. The volume at 40 s is 36.0 cm3 and at 70 s is 63.0 cm3. Calculate the rate during this section in cm3 s^-1 and give the unit in final answer.

(Total for Question 14 is 2 marks)

Explain, with reference to collision theory, how increasing concentration of acid affects the rate of the reaction between hydrochloric acid and magnesium ribbon in a gas syringe experiment. In your answer include a clear chain of reasoning linking concentration to collision frequency, probability of successful collisions and observed rate.

(Total for Question 15 is 6 marks)

Mark scheme · IG.C10 Rates of Reaction: Collision Theory and Measuring Rate

Question 1

B1 particles must collide with sufficient energy (≥ activation energy) and with the correct orientation
Answer: They must collide with enough energy (at least the activation energy) and with a suitable orientation

Question 2

B1 increasing concentration increases the number of particles per unit volume so collisions are more frequent
B1 more frequent collisions lead to a higher rate of reaction
Answer: Higher concentration means more particles per unit volume so collisions happen more often, increasing the reaction rate

Question 3

B1 higher temperature gives particles more kinetic energy so they move faster and collide more often
B1 higher energy means a larger proportion of collisions have energy ≥ activation energy, so more successful collisions
Answer: Raising temperature increases particle speed so collisions are more frequent, and increases collision energy so a greater fraction exceed the activation energy, raising the rate

Question 4

B1 control the mass or surface area of marble chips, to ensure the amount of reactive solid is the same
B1 control concentration and volume of acid, to ensure the number of acid particles available is the same
B1 control temperature, to prevent temperature changes affecting collision frequency and energy
Answer: Keep marble chip mass or particle size constant so the amount of solid is the same; keep acid concentration and volume constant so reactant quantity is constant; keep temperature constant so collision energy is unchanged

Question 5

B1 sketch: steep initial downward slope that becomes less steep and levels off towards a horizontal line
B1 description: mass decreases over time as CO2 gas is lost, rate is fastest at the start and slows as reactants are used up
B1 explain leveling: graph levels off when reaction is nearly complete and mass stops changing
Answer: Graph: mass falls quickly at first (steep negative slope) then the slope becomes less steep and the curve levels off to horizontal as reaction finishes

Question 6

B1 more accurate measurement of gas volume than inferring from mass loss
B1 gas syringe gives direct, continuous volume readings and is less affected by drafts or vibration
Answer: A gas syringe measures gas volume directly and continuously and is often more accurate and less affected by drafts or balance instability than measuring mass loss

Question 7

B1 disappearance time depends on rate at which reactant particles collide to form cloudy product so more frequent successful collisions give faster clouding
B1 suggestion: increase temperature or increase concentration or use smaller particle size if solids present
B1 link: increasing temperature or concentration raises collision frequency and energy so time is reduced
Answer: The cross disappears faster when particles collide more often or with more energy; increasing temperature or concentration will increase collision frequency and energy and so speed the reaction

Question 8

M1 calculates change in volume: 24.0 - 12.0 = 12.0 cm3
M1 divides by time interval 20 s to find rate
A1 gives mean rate = 0.60 cm3 s^-1 cao with units
Answer: Mean rate = 12.0 cm3 / 20 s = 0.60 cm3 s^-1

Question 9

M1 calculates change in mass: 52.00 - 51.35 = 0.65 g
M1 divides by time interval 60 s to find rate
A1 gives mean rate = 0.0108 g s^-1 cao to 3 s.f. as 0.0108 g s^-1
Answer: Mean rate = 0.65 g / 60 s = 0.0108 g s^-1 (3 s.f.)

Question 10

B1 initial rate found by drawing a tangent at time zero and finding its gradient (change in volume / change in time)
B1 physically represents the rate when reactant concentrations are at their initial values, the fastest rate
Answer: Draw a tangent at t = 0 and calculate its gradient (delta volume / delta time); it represents how fast gas is produced at the start when reactant concentrations are highest

Question 11

M1 adds times: 32.0 + 28.5 + 30.5 = 91.0 s
M1 divides by 3 to find mean = 30.333... s
A1 gives mean time = 30.3 s cao to 3 s.f.
B1 states reason: to improve reliability by reducing effect of random error or anomalies
Answer: Mean = (32.0 + 28.5 + 30.5) / 3 = 30.3 s; repeating improves reliability and reduces the effect of random error

Question 12

B1 states that a catalyst provides an alternative reaction pathway
B1 states that the alternative pathway has a lower activation energy so more collisions are successful
B1 links to collision theory: with lower activation energy a larger proportion of collisions have sufficient energy to react
B1 may state that the catalyst is not used up at the end of the reaction
Answer: A catalyst provides an alternative pathway with lower activation energy so a larger fraction of collisions are successful, increasing the rate; the catalyst is not consumed

Question 13

B1 prediction: initial rate will increase
B1 explanation: smaller particles give larger total surface area so more frequent collisions at the surface
Answer: Initial rate increases because smaller particles give a larger surface area for the same mass, increasing collision frequency with acid

Question 14

M1 calculates change in volume 63.0 - 36.0 = 27.0 cm3 and change in time 30 s
A1 gives rate = 0.90 cm3 s^-1 cao with unit
Answer: Rate = 27.0 cm3 / 30 s = 0.90 cm3 s^-1

Question 15

Level 1 (1-2): Basic statements about concentration and rate with little or no reference to collision theory or lacking links between ideas
Level 2 (3-4): Some correct chemistry and partial chain of reasoning: states that higher concentration gives more particles and more collisions, with limited explanation of why collisions are more likely to be successful
Level 3 (5-6): A full, logical chain using collision theory: increasing concentration increases particle number per unit volume, raising collision frequency; explains that this increases the number of collisions per second and, therefore, the number of collisions with energy >= activation energy, so the measured gas production rate increases; may mention units and that magnesium is solid so collisions occur at the surface
Indicative content:
- Increasing acid concentration increases the number of acid particles per unit volume
- More particles per unit volume means a higher collision frequency between acid particles and magnesium surface atoms
- Higher collision frequency increases the number of collisions per second that could lead to reaction
- A larger number of collisions raises the number of successful collisions per second, so the rate of hydrogen gas production increases
- For a solid magnesium ribbon the active collisions occur at the surface, so concentration affects how often acid particles strike the metal surface
- Clear linking sentences that show how the observed increase in slope on a volume-time graph or increased gradient from mass loss follows from more successful collisions

Rates of Reaction: Collision Theory and Measuring Rate - Worksheets, Questions and Revision