This question is about equilibria - AQA - A-Level Chemistry - Question 1 - 2022 - Paper 1
Question 1
This question is about equilibria.
1. Give two features of a reaction in dynamic equilibrium.
Feature 1
Feature 2
2. A gas-phase reaction is at equilibrium.
When... show full transcript
Worked Solution & Example Answer:This question is about equilibria - AQA - A-Level Chemistry - Question 1 - 2022 - Paper 1
Step 1
Give two features of a reaction in dynamic equilibrium.
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Answer
The rates of the forward and reverse reactions are equal.
The concentrations of the reactants and products remain constant over time.
Step 2
State what can be deduced about the chemical equation for this equilibrium.
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Answer
The reaction favors the production of reactants when pressure is increased, indicating that there are more moles of gaseous products than gaseous reactants.
Step 3
Calculate the amount, in moles, of carbon monoxide present at equilibrium.
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Answer
At equilibrium, the total number of moles is given by the sum of moles of all species:
Total moles = 0.430 mol (CO) + 0.860 mol (H2) - 0.110 mol (CH3OH)
Total moles = 1.180 mol.
Using the mole fraction of CO:
Mole fraction of CO = rac{0.430}{1.180} = 0.364.
Thus, the moles of carbon monoxide present at equilibrium is approximately 0.052 mol.
Step 4
Calculate the partial pressure, in kPa, of carbon monoxide present in this equilibrium mixture.
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Answer
Using the ideal gas law and Dalton's law, we can find the partial pressure:
Partial pressure of CO = Mole fraction of CO * Total pressure = 0.364 * 250 kPa ≈ 91.0 kPa.
Step 5
Give an expression for the equilibrium constant (Kc) for this reaction.
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Answer
K_c = rac{[CH3OH]}{[CO][H2]^2}.
Step 6
Calculate the partial pressure, in kPa, of hydrogen in this equilibrium mixture.
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Answer
Using the values given in Table 1:
K_c = rac{P_{CH3OH}}{P_{CO} imes P_{H2}^2}.
Substituting the known values:
1.15 x 10^{-4} = rac{5.45}{125 imes P_{H2}^2}.
Solving for P_{H2} gives approximately 0.45 kPa.
Step 7
Give the units for Kc.
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