This question is about reversible reactions and chemical equilibrium - AQA - GCSE Chemistry - Question 6 - 2015 - Paper 3
Question 6
This question is about reversible reactions and chemical equilibrium.
(a) Reversible reactions can reach equilibrium in a closed system.
(a) (i) What is meant by a... show full transcript
Worked Solution & Example Answer:This question is about reversible reactions and chemical equilibrium - AQA - GCSE Chemistry - Question 6 - 2015 - Paper 3
Step 1
What is meant by a closed system?
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Answer
A closed system is one where nothing can enter or leave during the reaction. This means that the total amount of reactants and products remains constant, as the matter is contained entirely within the system.
Step 2
Explain why, when a reversible reaction reaches equilibrium, the reaction appears to have stopped.
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Answer
At equilibrium, the rates of the forward and backward reactions are equal, meaning there is no net change in the concentrations of reactants and products. Although the reactions continue to occur, they do so at equal rates, which leads to the appearance that the reaction has stopped.
Step 3
Name a natural resource from which hydrogen is produced.
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Natural gas is a significant natural resource from which hydrogen is produced. Other options include methane (CH₄) and water.
Step 4
Explain how a catalyst speeds up a reaction.
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A catalyst provides an alternative pathway for the reaction with a lower activation energy. This means that more particles have sufficient energy to react, increasing the rate of reaction without being consumed in the process.
Step 5
What happens to the amount of ammonia produced at equilibrium if the pressure is increased? Give a reason for your answer.
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The amount of ammonia produced at equilibrium will increase. This occurs because increasing the pressure shifts the equilibrium position towards the side of the reaction with fewer gas molecules. In this case, the forward reaction produces fewer gas molecules.
Step 6
Draw an arrow to show the activation energy on the diagram in Figure 3.
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The arrow should be drawn from the energy level of 2HI to the peak of the energy curve in the diagram, indicating the activation energy required for the forward reaction.
Step 7
How does the diagram in Figure 3 show that the reaction is endothermic?
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The diagram shows that the energy level of the products (H₂ and I₂) is higher than that of the reactants (2HI), indicating that energy is absorbed in the forward reaction, which is characteristic of endothermic reactions.
Step 8
Suggest what effect, if any, increasing the temperature will have on the amount of hydrogen iodide at equilibrium. Give a reason for your answer.
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Increasing the temperature will decrease the amount of hydrogen iodide at equilibrium. This is because, in an endothermic reaction, raising the temperature shifts the equilibrium position in the direction that absorbs heat, which in this case is the forward reaction that produces hydrogen and iodine, thus reducing the concentration of reactants.
