Grade 12 Physical Sciences · Chemical Change · Paper 2 (Chemistry)

Chemical Equilibrium Grade 12

Real Chemical Equilibrium past paper questions and answers from 2024 to 2025, with each memo split into the ticks examiners give. Try one, mark yourself, and see exactly which skill cost you marks.

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Question 1.5 · 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.

1.5 The following reaction reaches equilibrium in a closed container:

H_{2} (g) + S(s) ⇌ H_{2} S(g)

Δ H < 0

The reaction rate versus time graph for the reaction is given below.

What change was made to the system at time

t_{1}

?(2)

A The pressure was increased at a constant temperature.
B The volume of the container was increased.
C The temperature was increased.
D More hydrogen was added to the system.

Work it out on paper first. Then mark yourself with the official memo, one tick at a time.

Chemical Equilibrium skills

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More Chemical Equilibrium Grade 12 questions and answers

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4. Question 4.2.1 · November 2025 · Paper 1 · National (DBE) · 3 marks
Cricketers at an academy conduct an experiment to determine the relationship between the contact time and the final momentum of a ball for a constant average net force.

A cricket ball of mass $150$ g is thrown horizontally with a certain initial velocity and is struck by a bat so that the ball moves in the opposite direction, as shown in the diagram below. The average net force acting on the ball is horizontal.

The experiment is repeated using the same ball. The average net force and the initial velocity of the ball are kept constant. The contact time between the bat and the ball is changed EACH time. The results obtained are shown in the sketch graph below.
4.2 Calculate the:
4.2.1 Average net force acting on the ball(3)
Show the memo (3 ticks)Memo
1. ✓
  METHOD 1: Change in final momentum (numerator)Gradient $= F_{n e t} = \frac{Δ p _{f}}{Δ ( Δ t )}$
  $= \frac{4 , 5 - 0}{\dots}$
  1 mark · Read a graph of results
2. ✓
  METHOD 1: Change in contact time (denominator) $F_{n e t} = \frac{4 , 5 - 0}{0 , 03 - 0 , 01} = 225$ N
  1 mark · Read a graph of results
3. ✓
  METHOD 1: Answer with direction $F_{n e t} = 225$ N to the right / opposite to the original direction of the ball
  1 mark · Read a graph of results
5. Question 6.1.1 · November 2025 · Paper 2 · National (DBE) · 2 marks
6.1 Equilibrium is established at $25$ °C in a saturated calcium hydroxide solution according to the reaction:

$Ca(OH)_{2} (s) ⇌ Ca^{2 +} (aq) + 2 OH^{-} (aq)$

Answer the questions that follow.
6.1.1 State Le Chatelier's principle.(2)
Show the memo (1 tick)Memo
1. ✓
  Le Chatelier's principleWhen the equilibrium in a closed system is disturbed, the system will re-instate a new equilibrium by favouring the reaction that will cancel/oppose the disturbance.
  2 marks · State equilibrium principle and terms
6. Question 10.3.2 · May/June 2025 · Paper 1 · National (DBE) · 4 marks
Light of different frequencies is incident on a metal plate. The sketch graph below shows the relationship between the maximum kinetic energy, $E_{k (ma x)}$ , of the photoelectrons and the energy of the incident photons.
10.3 Calculate the:
10.3.2 Value of Y(4)
Show the memo (4 ticks)Memo
1. ✓
  METHOD 1: Formula $E = W_{0} + E_{k (ma x)}$ (or $h f = W_{0} + E_{k (ma x)}$ )
  1 mark · Use the photoelectric equation
2. ✓
  METHOD 1: Work function $= 3, 68 \times 1 0^{- 19} + \dots$
  1 mark · Use the photoelectric equation
3. ✓
  METHOD 1: Kinetic energy $= 3, 68 \times 1 0^{- 19} + 2, 99 \times 1 0^{- 19}$
  1 mark · Use the photoelectric equation
4. ✓
  METHOD 1: Answer $E = 6, 67 \times 1 0^{- 19}$ (J)
  1 mark · Use the photoelectric equation
7. Question 1.5 · November 2024 · Paper 2 · National (DBE) · 2 marks
Various options are provided as possible answers to the following questions. Each question has only ONE correct answer. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.10) in the ANSWER BOOK, e.g. 1.11 E.
1.5 Initially, an equal number of moles of hydrogen gas, $H_{2}$ (g), and iodine gas, $I_{2}$ (g), are mixed in a closed container. The reaction reaches equilibrium at a constant temperature according to the balanced equation.

$H_{2} (g) + I_{2} (g) ⇌ 2 HI(g)$

Which ONE of the following is ALWAYS TRUE at equilibrium?(2)
1. A $[H_{2}] = [I_{2}]$
2. B $[HI] = [I_{2}]$
3. C $[HI] = 2 [H_{2}]$
4. D $[H_{2}] = [I_{2}] = [HI]$
Show the memo (1 tick)Memo
1. ✓
  Correct option $H_{2}$ and $I_{2}$ start with equal amounts and react in a $1 : 1$ ratio, so the same amount $x$ of each is used. At equilibrium both are $n - x$ : $[H_{2}] = [I_{2}]$ always.
  How much HI forms depends on $K_{c}$ , so B, C and D are true only for particular values of $K_{c}$ .
  
  Answer: A
  2 marks · Complete an equilibrium table
8. Question 6.1.1 · November 2024 · Paper 2 · National (DBE) · 2 marks
6.1 The reaction of carbon monoxide gas, CO(g), with oxygen gas, $O_{2}$ (g), is investigated. The reaction reaches equilibrium in a closed container at constant temperature T °C, according to the balanced equation:

$2 CO(g) + O_{2} (g) ⇌ 2 CO_{2} (g)$ $Δ H < 0$

Changes to the conditions of equilibrium are made at different times. The graph shows the results obtained. X, Y and Z represent the gases in the above reaction.

Answer the questions that follow.
6.1.1 Define the term chemical equilibrium.(2)
Show the memo (1 tick)Memo
1. ✓
  Definition of chemical equilibrium(The dynamic equilibrium when) the rate of the forward reaction equals the rate of the reverse reaction.
  
  OR: The stage in a chemical reaction when the concentrations of the reactants and products remain constant.
  2 marks · State equilibrium principle and terms
9. Question 1.5 · May/June 2024 · Paper 2 · National (DBE) · 2 marks
1.5 The balanced equation below represents a reaction at equilibrium.

$2 CrO_{4}^{2 -} (aq) + 2 H_{3} O^{+} (aq) ⇌ Cr_{2} O_{7}^{2 -} (aq) + 3 H_{2} O (ℓ)$
( $CrO_{4}^{2 -}$ is yellow; $Cr_{2} O_{7}^{2 -}$ is orange.)

Which statement(s) is/are TRUE when a few drops of concentrated hydrochloric acid, HCℓ(conc), are added to the mixture?

(i) The reverse reaction will be favoured.
(ii) The concentration of $Cr_{2} O_{7}^{2 -}$ (aq) increases.
(iii) The colour of the solution changes from yellow to orange.(2)
1. A (i) only
2. B (i) and (ii) only
3. C (i) and (iii) only
4. D (ii) and (iii) only
Show the memo (1 tick)Memo
1. ✓
  Choose the correct optionAdding HCℓ increases $[H_{3} O^{+}]$ , a reactant. The system uses up some of the added $H_{3} O^{+}$ by favouring the FORWARD reaction. So (i) is false, $[Cr_{2} O_{7}^{2 -}]$ increases (ii) and the solution turns from yellow to orange (iii).
  
  Answer: D
  2 marks · Apply Le Chatelier's principle
10. Question 4.1.3 · May/June 2024 · Paper 2 · National (DBE) · 2 marks
4.1 In an experiment, a test tube containing methanol, propanoic acid and a catalyst is heated in a water bath, as shown below.

Write down:
4.1.3 TWO reasons why the use of a water bath is preferred in this experiment(2)
Show the memo (2 ticks)Memo
1. ✓
  First reasonAlcohol/methanol/reactant is flammable/catches fire easily.
  1 mark · Describe and evaluate an experiment
2. ✓
  Second reasonTo heat evenly / a steady, controlled, gradual increase in temperature. (OR: Alcohol/methanol will evaporate too quickly/is volatile.)
  1 mark · Describe and evaluate an experiment

Chemical Equilibrium Grade 12 videos

Short lessons from South African teachers first. Videos load only when you tap play, to save your data.

Chemical Equilibrium Introduction Grade 12 ChemistryMiss Martins Maths and Science

KC grade 12: IntroductionKevinmathscience

KC grade 12: Table IntroductionKevinmathscience

Equilibrium Constant Grade 12: ExamKevinmathscience

Le Chatelier's Principle grade 12: IntroductionKevinmathscience

Equilibrium Graphs grade 12: IntroductionKevinmathscience

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