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This question is about equilibria - AQA - A-Level Chemistry - Question 1 - 2022 - Paper 1

Question 1

This question is about equilibria. 0 1.1. Give two features of a reaction in dynamic equilibrium. Feature 1 Feature 2 0 1.2. A gas-phase reaction is at ... 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, meaning there is no net change in the concentrations of reactants and products.
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 involves a decrease in the number of moles of gaseous products compared to the gaseous reactants, indicating that an increase in pressure favors the side of the reaction with fewer moles (more moles on the right-hand side).

Step 3

Calculate the amount, in moles, of carbon monoxide present at equilibrium.

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Answer

To find the amount of carbon monoxide, we first calculate the total moles at equilibrium:

Total moles = 0.430 mol (CO) + 0.860 mol (H2) - 0.110 mol (CH3OH) = 1.180 mol

Using the reaction stoichiometry, we note the mole ratio: At equilibrium, if x is the amount of CO reacted, we have:

CO remaining = 0.430 - x H2 remaining = 0.860 - 2x

The equilibrium expression related to the total pressure can be used to find x after determining the total pressure contribution of each gas.

Step 4

Calculate the partial pressure, in kPa, of carbon monoxide in this equilibrium mixture.

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Answer

The equilibrium expression relates to the total pressure (P) calculated from the total moles:

o P_{CO} = (n_{CO}/n_{total}) imes P_{total}

By identifying the amounts, we find: P_{CO} = (0.320 mol / 1.07 mol) × 250 kPa = 74.5 kPa.

Step 5

Give an expression for the equilibrium constant (Kc) for this reaction.

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Answer

The equilibrium constant expression (Kc) is given by:

$K_c = \frac{[CH_3OH]}{[CO][H_2]^2}$

Concentrations should be expressed in mol/L.

Step 6

Calculate the partial pressure, in kPa, of hydrogen in this equilibrium mixture.

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Answer

Using the previously given partial pressures: Kc = (5.45 kPa) / (125 kPa * P_H2^2),

Reorganizing provides: P_H2^2 = (5.45 kPa) / (1.15 × 10^4 kPa^-2)

Calculating gives the value for P_H2.

Step 7

Give the units for Kc'.

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Answer

The units for Kc' when relating concentrations will be kPa^-2.

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This question is about equilibria - AQA - A-Level Chemistry - Question 1 - 2022 - Paper 1

Worked Solution & Example Answer:This question is about equilibria - AQA - A-Level Chemistry - Question 1 - 2022 - Paper 1

Give two features of a reaction in dynamic equilibrium.

State what can be deduced about the chemical equation for this equilibrium.

Calculate the amount, in moles, of carbon monoxide present at equilibrium.

Calculate the partial pressure, in kPa, of carbon monoxide in this equilibrium mixture.

Give an expression for the equilibrium constant (Kc) for this reaction.

Calculate the partial pressure, in kPa, of hydrogen in this equilibrium mixture.

Give the units for Kc'.

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