Grade 11 Physical Sciences · Chemical Change

Define rate and energy terms

Give the exact meaning of words like exothermic, endothermic, activation energy, activated complex, reaction rate and catalyst.

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Energy and Chemical Change grade 11: Activation energy, heat of reaction, catalyst and MORE!Miss Martins Maths and Science

Energy and chemical change Grade 11 Chemistry | Introduction and OverviewMiss Martins Maths and Science

What Are Endothermic & Exothermic Reactions | Chemistry | FuseSchoolFuseSchool - Global Education

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Question 5.1 · May/June 2025 · Paper 2 · National (DBE) · 2 marks

The reaction between magnesium carbonate pellets,

MgCO_{3}

(s), and EXCESS dilute hydrochloric acid, HCℓ(aq), is used to investigate the effect of concentration on the rate of a reaction.

MgCO_{3} (s) + 2 HC ℓ (aq) \to MgC ℓ_{2} (aq) + H_{2} O (ℓ) + CO_{2} (g)

The apparatus used for this investigation is shown below. Diagram for this question

5.1 Define the term rate of reaction.(2)

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More past paper questions: define rate and energy terms

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3. Question 5.3.2 · November 2025 · Paper 2 · National (DBE) · 2 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.
5.3.2 Define the term activated complex.(2)
Show the memo (1 tick)Memo
1. ✓
  Definition of activated complexUnstable (high energy) transition state from reactants to products.
  ACCEPT: Unstable (high energy) transition state between reactants and products.
  2 marks · Define rate and energy terms
4. Question 5.1.1 · November 2024 · Paper 2 · National (DBE) · 2 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.
5.1.1 Define the term reaction rate.(2)
Show the memo (1 tick)Memo
1. ✓
  Definition of reaction rateChange in concentration of products/reactants per (unit) time.
  2 marks · Define rate and energy terms
5. Question 5.1 · May/June 2022 · Paper 2 · National (DBE) · 2 marks
Learners use the reaction of $MgCO_{3}$ (s) with EXCESS dilute HC $ℓ$ (aq) to investigate the relationship between temperature and the rate of a chemical reaction.

The balanced equation for the reaction is:

$MgCO_{3} (s) + 2 HC ℓ (aq) \to MgC ℓ_{2} (aq) + CO_{2} (g) + H_{2} O (ℓ)$

The results obtained are represented in the graph below.
5.1 Define the term rate of reaction.(2)
Show the memo (2 ticks)Memo
1. ✓
  Change in concentrationChange in concentration
  1 mark · Define rate and energy terms
2. ✓
  Per unit timeof products/reactants per (unit) time.
  1 mark · Define rate and energy terms
6. Question 1.4 · November 2022 · 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 Which ONE of the following statements is the CORRECT definition for the rate of a reaction?(2)
1. A The time taken for the reaction to take place
2. B The speed at which the reaction takes place
3. C The rate of change in concentration of the products or reactants
4. D The rate of change in concentration of the products or reactants per unit time
Show the memo (1 tick)Memo
1. ✓
  Correct optionReaction rate is the change in concentration of reactants or products per unit time, i.e. the RATE OF CHANGE in concentration. Option C states this. Option D says 'rate of change ... per unit time', which counts time twice (a rate already means per unit time).
  
  Answer: C
  2 marks · Define rate and energy terms

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