AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Foundation), 2022: Question 3

8 marks · Low Demand difficulty · Short Answer

Answer questions about ammonia, reversible reactions, equilibrium, catalysts, and formulations.

Practise this question

Question

The image shows a series of questions about ammonia and its compounds. It includes a chemical equation for the thermal decomposition of ammonium chloride into ammonia and hydrogen chloride, a table of state symbols, a reaction profile graph (Figure 5) showing energy levels for reactants and products with two different activation energy curves (labeled A, B, C, D), and several fill-in-the-blank or tick-box questions.
Question text

03 This question is about ammonia and its compounds.

A student heated a sample of ammonium chloride.

The equation for the reaction is:

NH4Cl ⇌ NH3 + HCl

ammonium chloride ammonia

03.1 One product is ammonia.

What is the name of the product with the formula HCl?

[1 mark]

03.2 Ammonia is a gas.

What is the state symbol for ammonia?

[1 mark]

Tick ( ) one box.

(aq) (g) (I) (s)

03.3 How does the equation show that the reaction is reversible?

[1 mark]

03.4 Complete the sentence.

[1 mark]

The forward reaction is endothermic,

so the reverse reaction is .

03.5 Complete the sentence.

Choose the answer from the box.

[1 mark]

concentration rate temperature

Equilibrium is reached when the forward and reverse reactions happen at exactly the

same .

The industrial process to produce ammonia uses a catalyst.

03.6 Figure 5 shows the reaction profile for the reaction with and without a catalyst.

Figure 5

Which letter represents the activation energy for the reaction with a catalyst?

[1 mark]

Tick ( ) one box.

A B 11C D

03.7 Give one reason why using a catalyst reduces costs.

Do not answer in terms of activation energy.

[1 mark]

03.8 Ammonia is in a mixture that is used as a household cleaner.

What is a mixture that has been designed as a useful product called?

[1 mark]

Mark scheme

Show the mark scheme The mark scheme provides answers for eight sub-questions. Key answers include 'hydrogen chloride' for HCl, '(g)' for the state symbol of ammonia gas, the reversible reaction symbol, 'exothermic' for the reverse of an endothermic reaction, 'rate' for the condition of equilibrium, 'C' for activation energy with a catalyst, and 'formulation' for a designed mixture. It also lists assessment objectives and specification references for each part.

Question 3

AO /

Question Answers Extra information Mark

Spec. Ref.

03.1 hydrogen chloride allow hydrochloric acid 1 AO1

5.6.2.1

AO /

Spec. Ref.

03.2 (g) 1 AO1

5.2.2.2

AO /

Spec. Ref.

03.3 ⇌ allow reversible sign / arrow 1 AO1

5.6.2.1

AO /

Spec. Ref.

03.4 exothermic 1 AO1

5.6.2.2

AO /

Spec. Ref.

03.5 rate 1 AO1

5.6.2.3

AO /

Spec. Ref.

03.6 C 1 AO1

5.6.1.4

AO /

Spec. Ref.

03.7 any one from: 1 AO1

• increases rate of reaction 5.6.1.4

• reduces energy required

• lower temperature can be

used

AO /

Spec. Ref.

03.8 formulation 1 AO1

5.8.1.2

Total Question 3 8

How to answer it

Ammonia, Reversible Reactions, and Catalysts

What this question tests

This question assesses your fundamental understanding of chemical equations, reversible reactions, energy changes, reaction profiles, and the industrial role of catalysts and formulations.

Parts 03.1 & 03.2: Chemical Naming and State Symbols

Correct Answers

  • 03.1: Hydrogen chloride (or hydrochloric acid)
  • 03.2: (g)

Key Knowledge

State symbols tell us the physical state of a substance:

  • (s): Solid
  • (l): Liquid
  • (g): Gas
  • (aq): Aqueous (dissolved in water)

Parts 03.3 & 03.4: Reversible Reactions

Understanding the ⇌ symbol

Correct Answers

  • 03.3: The double arrow symbol (⇌)
  • 03.4: Exothermic

Exam Technique

In 03.4, remember the rule: If a reversible reaction is endothermic in one direction, it must be exothermic in the opposite direction by the exact same amount of energy.

Part 03.5: Defining Equilibrium

Correct Answer

rate

Common Errors

Students often confuse rate with concentration. At equilibrium, the rates are equal, but the concentrations of reactants and products are usually different (though they remain constant).

Part 03.6: Reaction Profiles

Identifying Activation Energy

Correct Answer

C

Key Knowledge

A catalyst provides an alternative pathway with a lower activation energy. On a graph:

  • B is the activation energy without a catalyst (the higher peak).
  • C is the activation energy with a catalyst (the lower peak).
  • A is the overall energy change (enthalpy change).

Part 03.7: Economic Benefits of Catalysts

Correct Answers (Any one)

  • Reduces energy required
  • Lower temperature can be used
  • Increases the rate of reaction

⚠️ Read the Instruction!

The question explicitly says: "Do not answer in terms of activation energy." Even though catalysts lower activation energy, you will get 0 marks if you write that here. Focus on the cost/energy implications instead.

Part 03.8: Formulations

Correct Answer

formulation

Key Knowledge

A formulation is a mixture that has been designed as a useful product. Every ingredient is added in a specific quantity to ensure the product has the required properties (e.g., medicines, paints, fuels, cleaners).

Topics

Chemistry · C6: The Rate and Extent of Chemical Change · C2: Bonding, Structure and the Properties of Matter · C8: Chemical Analysis · C4: Chemical Changes

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 2 (Foundation), 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.