Grade 12 Physical Sciences · Chemical Change

State equilibrium principle and terms

State Le Chatelier's principle in full, or define dynamic equilibrium, a closed system or a reversible reaction.

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Chemical Equilibrium Introduction Grade 12 ChemistryMiss Martins Maths and Science

Le Chatelier's Principle grade 12: IntroductionKevinmathscience

Chemical Equilibrium Forward and Reverse Reaction Grade 12 ChemistryMiss Martins Maths and Science

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Question 6.1 · May/June 2024 · Paper 2 · National (DBE) · 2 marks

Consider the balanced equation for a hypothetical reaction that takes place in

2

^{3}

sealed containers.

P_{2} Q(g) + 3 Q(s) ⇌ 2 PQ_{2} (g)

The graphs below, not drawn to scale, are obtained for the same reaction at two different temperatures.

Graph A is obtained at

298

K and graph B at

398

6.1 State Le Chatelier's principle.(2)

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

More past paper questions: state equilibrium principle and terms

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3. 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
4. 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
5. Question 6.1 · May/June 2023 · Paper 2 · National (DBE) · 2 marks
One mole of pure hydrogen iodide gas, HI(g), is sealed in a $1$ dm $^{3}$ container at $721$ K. Equilibrium is reached according to the following balanced equation:

$2 HI(g) ⇌ H_{2} (g) + I_{2} (g)$

It is found that $0, 11$ moles of $I_{2}$ (g) are present at equilibrium.
6.1 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 6.1.2 · May/June 2022 · Paper 2 · National (DBE) · 2 marks
6.1 Initially, $4$ moles $H_{2}$ (g) and $4$ moles $I_{2}$ (g) are allowed to react in a sealed $2$ dm $^{3}$ flask according to the following balanced equation:

$H_{2} (g) + I_{2} (g) ⇌ 2 HI(g)$ $Δ H < 0$

The graph below shows the concentrations of $H_{2}$ (g) and HI(g) versus time during the reaction.

Answer the questions that follow.
6.1.2 State Le Chatelier's principle.(2)
Show the memo (2 ticks)Memo
1. ✓
  Disturbed closed system re-instates equilibriumWhen the equilibrium in a closed system is disturbed, the system will re-instate a (new) equilibrium
  1 mark · State equilibrium principle and terms
2. ✓
  Favours the reaction that opposes the disturbanceby favouring the reaction that will cancel/oppose the disturbance.
  1 mark · State equilibrium principle and terms

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