Reversible Reactions and Equilibrium (qualitative)
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Reversible Reactions and Equilibrium (qualitative) — Free MYP4 Chemistry Practice Questions

1QuestionEffect of changes in conditions (temperature, concentration – basic idea)Concept Practice
2 marks~3 minCriterion A
The Haber process produces ammonia via the following reversible reaction:

N2(g)+3H2(g)⇌2NH3(g)\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)
a
Explain what the symbol ⇌\rightleftharpoons indicates about this reaction, referring to the forward reaction and the reverse reaction. Use the state symbols in your answer. [1]
b
Explain what is meant by the term equilibrium in the context of this reaction. [1]
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Solutions

2QuestionDefinition of reversible reactionsAssessment Practice
4 marks~6 minCriterion C
When blue hydrated copper(II) sulfate crystals, CuSO4⋅5H2OCuSO_4 \cdot 5H_2O, are heated, they decompose to form white anhydrous copper(II) sulfate, CuSO4CuSO_4, and water vapour. When water is added to the white powder, the blue colour is restored.

The diagram shows both a forward arrow (heating) and a reverse arrow (adding water) between the two forms.
a
Explain why the copper(II) sulfate reaction shown in the diagram is described as reversible. [2]
b
A student claims that heating alone is sufficient to determine the direction of any reversible reaction. Using the copper(II) sulfate system, explain why this claim is incorrect. [2]
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3QuestionClosed system requirement for equilibriumAssessment Practice
7 marks~11 minCriterion B
A student investigates the equilibrium between nitrogen dioxide and dinitrogen tetroxide in a sealed syringe:

2 NO2(g)⇌N2O4(g)ΔH=−58 kJ mol−12\,\text{NO}_2\text{(g)} \rightleftharpoons \text{N}_2\text{O}_4\text{(g)} \quad \Delta H = -58 \text{ kJ mol}^{-1}

Different amounts of NO2_2 are injected and, after equilibrium is reached at constant temperature, concentrations are recorded:

Injection12345
[NO2]eq[\text{NO}_2]_{eq} (M)0.100.200.350.550.80
[N2O4]eq[\text{N}_2\text{O}_4]_{eq} (M)0.050.100.180.280.41
a
Construct a graph of [N2O4]eq[\text{N}_2\text{O}_4]_{eq} (y-axis) against [NO2]eq[\text{NO}_2]_{eq} (x-axis) and interpret the relationship shown. [2]
b
Deduce the equilibrium concentration of N2_2O4_4 when [NO2]eq=1.00[\text{NO}_2]_{eq} = 1.00 M. Show your method clearly. [2]
c
Analyse why [N2O4]eq[\text{N}_2\text{O}_4]_{eq} does not increase in direct proportion to [NO2]eq[\text{NO}_2]_{eq}, using both the equilibrium expression for this reaction and collision theory. [3]
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Solutions

4QuestionClosed system requirement for equilibriumAssessment Practice
10 marks~15 minCriterion D
The Haber–Bosch process produces ammonia (NH3\text{NH}_3) for synthetic fertilizers in a closed system at approximately 200 atm and 450°C using an iron catalyst:

N2(g)+3H2(g)⇌2NH3(g)ΔH=−92 kJ mol−1\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)} \quad \Delta H = -92 \text{ kJ mol}^{-1}

Hydrogen is sourced from natural gas via steam methane reforming, releasing approximately 1.9 tonnes of CO2\text{CO}_2 per tonne of NH3\text{NH}_3 produced. The process currently supports food production for roughly half the world's population.
a
Explain why a closed system is necessary for equilibrium to be established, and explain how operating at 200 atm increases the yield of NH3\text{NH}_3. [3]
b
Discuss the relationship between the Haber–Bosch process and global food security, referring to both the scale and the mechanism of its contribution. [3]
c
Evaluate the environmental impact of the Haber–Bosch process, considering both energy consumption and CO2\text{CO}_2 emissions, and assess whether the societal benefits justify continuing the process in its current form. [4]
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