Grade 12 Physical Sciences · Chemical Change

Explain rate using collision theory

Explain how temperature, concentration, surface area or a catalyst changes reaction rate using particle collisions (powder reacts faster than lumps).

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Collision Theory grade 12: Part 1Kevinmathscience

Rate of reaction: Factors affecting the rate of reaction Grade 12 ChemistryMiss Martins Maths and Science

Collision Theory grade 12: Part 2Kevinmathscience

Collision Theory Grade 12 Rate and extent of reaction Gr 12 ChemistryMiss Martins Maths and Science

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Question 1.4 · November 2025 · Paper 2 · National (DBE) · 2 marks

Various options are provided as possible answers to the following questions. Each question has only ONE correct answer.

1.4 Magnesium ribbon of mass

2

g reacts with excess hydrochloric acid of concentration

0, 1

mol·dm

^{- 3}

20

°C:

Mg(s) + 2 HC ℓ (aq) \to MgC ℓ_{2} (aq) + H_{2} (g)

Which ONE of the following changes will NOT increase the initial rate of the reaction?(2)

A Using 2 g of powdered magnesium
B Increasing the temperature of HC $ℓ$ to 30 °C
C Using a longer piece of the magnesium ribbon
D Doubling the volume of the hydrochloric acid used

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More past paper questions: explain rate using collision theory

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3. Question 5.3.3 · November 2025 · Paper 2 · National (DBE) · 3 marks
5.3 The reaction between sulphur dioxide, $SO_{2}$ (g), and oxygen, $O_{2}$ (g), takes place in a sealed container according to the balanced equation below.

$2 SO_{2} (g) + O_{2} (g) ⇌ 2 SO_{3} (g)$ $Δ H = - 196$ kJ·mol $^{- 1}$

Answer the questions that follow.
5.3.3 A catalyst, vanadium pentoxide, is added to the reaction. Explain, in terms of the collision theory, why the rate of the reaction will increase.(3)
Show the memo (3 ticks)Memo
1. ✓
  Lower activation energyCatalyst provides an alternative path with lower activation energy / lowers the activation energy.
  1 mark · Explain rate using collision theory
2. ✓
  More particles with enough energyMore particles have sufficient (kinetic) energy / kinetic energy greater than (or equal to) activation energy.
  1 mark · Explain rate using collision theory
3. ✓
  More effective collisions per unit timeMore effective collisions per unit time/second.
  OR Higher frequency of effective collisions.
  1 mark · Explain rate using collision theory
4. Question 1.4 · May/June 2025 · Paper 2 · National (DBE) · 2 marks
1.4 Two gases are added into each of four empty containers at the same temperature. The diagrams below show the molecules of the gases and the volumes of the containers at the start of the reaction.

In which ONE of the following containers is the initial reaction rate the highest?(2)
1. A Container A
2. B Container B
3. C Container C
4. D Container D
Show the memo (1 tick)Memo
1. ✓
  Correct optionCount the molecules per volume: A has 7 molecules in $5$ cm $^{3}$ , B has 5 in $5$ cm $^{3}$ , C has 7 in $10$ cm $^{3}$ and D has 14 in $20$ cm $^{3}$ . A has the most particles per unit volume (highest concentration), so the most effective collisions per unit time.
  
  Answer: A
  2 marks · Explain rate using collision theory
5. Question 5.1.3 · November 2024 · Paper 2 · National (DBE) · 4 marks
5.1 The reaction between pure aluminium, Aℓ(s), and EXCESS hydrochloric acid, HCℓ(aq), is used to investigate the factors that affect the rate of a reaction.

The balanced equation for the reaction is:

$2 A ℓ (s) + 6 HC ℓ (aq) \to 2 A ℓ C ℓ_{3} (aq) + 3 H_{2} (g)$

Answer the questions that follow.
Assume that the concentration of the HCℓ(aq) stays constant for the duration of the reaction.
5.1.3 Use the collision theory to explain the change in the reaction rate from t = 0 to t = 5 minutes.(4)
Show the memo (4 ticks)Memo
1. ✓
  Surface area decreasesThe surface area/contact area/mass/size of aluminium decreases.
  1 mark · Explain rate using collision theory
2. ✓
  Less particles exposedLess particles exposed.
  1 mark · Explain rate using collision theory
3. ✓
  Less effective collisions per unit timeLess effective collisions per unit time/second.
  
  OR: Lower frequency of effective collisions.
  1 mark · Explain rate using collision theory
4. ✓
  Reaction rate decreasesReaction rate decreases / Lower reaction rate / Reaction slows down.
  1 mark · Explain rate using collision theory
6. Question 5.3.2 · May/June 2024 · Paper 2 · National (DBE) · 3 marks
The reaction between aluminium and EXCESS sulphuric acid is used to investigate factors affecting rates of reactions.

$2 A ℓ (s) + 3 H_{2} SO_{4} (aq) \to A ℓ_{2} (SO_{4})_{3} (aq) + 3 H_{2} (g)$
5.3 INVESTIGATION III

In this investigation, 5 g of the same sample of IMPURE aluminium powder reacts with an EXCESS diluted $H_{2} SO_{4}$ at $60$ °C in each of three runs. The table below summarises the conditions and the results obtained. (Assume that the impurities do not react.)

$2 A ℓ (s) + 3 H_{2} SO_{4} (aq) \to A ℓ_{2} (SO_{4})_{3} (aq) + 3 H_{2} (g)$

Answer the questions that follow.
5.3.2 Use the collision theory to explain how the average rate of the reaction is affected in this investigation.(3)
Show the memo (3 ticks)Memo
1. ✓
  Particles per unit volumeMore ( $H_{2} SO_{4}$ ) particles per unit volume.
  1 mark · Explain rate using collision theory
2. ✓
  Effective collisions per unit timeMore effective collisions per unit time. / Higher frequency of effective collisions.
  1 mark · Explain rate using collision theory
3. ✓
  ConclusionHigher reaction rate.
  1 mark · Explain rate using collision theory

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