AQA A Level Chemistry

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A LevelChemistryAQATopic Questions5. Advanced Physical Chemistry (A Level only)5.3 Equilibrium constant (Kp) for Homogeneous Systems (A Level only)

5.3 Equilibrium constant (Kp) for Homogeneous Systems (A Level only)

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11 mark

What is the correct Kp expression for the following reaction?

2SO2 (g) + O2 (g) ⇌ 2SO3 (g)

  • K subscript straight p equals fraction numerator p squared SO subscript 3 over denominator p squared SO subscript 2. p straight O subscript 2 end fraction

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21 mark

The Kp expression for a reaction is Kp = fraction numerator p space CH subscript 3 OH over denominator p squared straight H subscript 2. p CO end fraction

What is the correct equation for the reaction?

  • CH3OH (g)  ⇋ CO (g) + 2H2 (g) 

  • 2CO (g) + 4H2 (g) ⇋ 2CH3OH (g)

  • CO (g) + 2H2 (g) ⇋ CH3OH (g) 

  • 2CO (g) + H2 (g) ⇋ 2CH3OH (g)

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31 mark

3.00 mol of gas A reacts with 4.00 moles of gas B in a sealed vessel of volume 1.0 dm3 and total pressure of 1.50 kPa an equilibrium is established which contains 2.00 moles of gas C. 

A + B ⇌ 2C

What is the mole fraction of gas B at equilibrium?

  • 0.29

  • 0.42

  • 0.75

  • 0.40

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41 mark

Equal volumes of nitrogen and hydrogen are introduced into a 1 dm3 container. At 80 oC, the following equilibrium is established:

N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

The partial pressures of the nitrogen and hydrogen are 0.25 kPa and 0.80 kPa respectively. The total pressure is 1.50 kPa

What is the partial pressure of the ammonia in kPa ?

  • 0.50

  • 0.53

  • 1.05

  • 0.45

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51 mark

When a sample dinitrogen tetroxide gas is heated in a fixed volume container, it dissociates into nitrogen dioxide gas:

N2O4 (g)  ⇌  2NO2 (g)          ΔH = 55.3 kJ mol-1

Which of the following changes causes an increase in the value of Kp ?

  • Adding more NO2

  • Decreasing the pressure

  • Raising the temperature

  • Using a catalyst

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11 mark

9.20 g of dinitrogen tetroxide, N2O4 (g), was heated to a temperature of 350 K at a pressure of 13.5 kPa and dissociated into nitrogen dioxide, NO2 (g).

N2O4 (g)   ⇌   2NO2 (g)

At equilibrium, 70 % of N2O4 (g) had dissociated.

What is the numerical value of Kp at 350 K?

  • 4.50

  • 22.05

  • 51.96

  • 0.02

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21 mark

3.00 moles of SO3 (g) are placed into a 8 dm3 container and heated to 1200 K.

2SO3 (g) ⇌ 2SO2 (g) + O2 (g)

At equilibrium, the mixture contained 0.58 moles of oxygen at a total pressure 3.45 x 106 Pa.

What is the value for Kp?

  • 4.50 x 10-6 Pa

  • 352302 Pa

  • 222 Pa

  • 222074 Pa 

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31 mark

Methanol can be produced by a multi-step process using methane and water as the starting materials. The first step is the production of synthesis gas, which is a mixture of carbon monoxide and hydrogen that is used to synthesise many chemicals including methanol.

 CH4 (g) + H2O (g) ⇋ CO (g) + 3H2 (g)      ∆H = +206 kJ mol-1

Which of the following changes would increase the value of Kp for this equilibrium?

  • Increasing temperature 

  • Increasing pressure 

  • Decreasing temperature

  • Decreasing pressure 

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41 mark

Chloromethane can be made from the following reaction. 0.80 moles of methanol and hydrogen chloride are added to the reaction container.

 CH3OH (g) + HCl (g) ⇌ CH3Cl (g) + H2O (g)

 At 120 ℃, the value for Kp is 6.00 x 103  

Which statement about the number of moles of reactants and products at equilibrium is correct?

  • The number of moles of CH3Cl and H2O is 0.79

  • The number of moles of CH3OH and HCl is 0.79

  • The number of moles of CH3Cl and H2O is 1.26

  • The number of moles of CH3OH and H2O is 0.79

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51 mark

What are possible Kp units for the decomposition of calcium carbonate?

 

  • No units

  • kPa-1

  • kPa-2

  • MPa

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11 mark

When dinitrogen tetroxide gas is heated, it dissociates into nitrogen dioxide gas:

N2O4 (g)  ⇌  2NO2 (g)

At a particular temperature, the equilibrium partial pressure of nitrogen dioxide was 0.67 kPa and dinitrogen tetroxide was 0.33 kPa.

What is the numerical value of Kp at this temperature?

  • 1.36

  • 0.49

  • 0.65

  • 2.03

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21 mark

When 5.00 mol of A reacts with 5.00 moles of B in a sealed vessel of volume 1 dm3 and total pressure of 1.5 kPa an equilibrium is established which contains 3.00 moles of C. 

A + B ⇌ 2C

What is the equilibrium partial pressure of A? 

  • 2.00 kPa

  • 0.525 kPa

  • 0.350 kPa 

  • 0.450 kPa

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31 mark

The temperature is increased on the following gaseous equilibrium

2SO2 (g) + O2 (g) ⇌ 2SO3 (g)        ΔH = -197 kJ mol-1

Which of the following is true?

  • The position of equilibrium moves to the right

  • The partial pressure of SO3 increases

  • The value of Kp  decreases

  • The mole fraction of SO2 decreases

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41 mark

At 80 oC, the following equilibrium is established:

N2 (g)   +  3H2 (g)    ⇌   2NH3 (g)

The partial pressures of the nitrogen, hydrogen and ammonia are 0.25 kPa, 0.80 kPa and 0.35 kPa respectively.

What is the numerical value of Kp at 80 oC?

  • 1.04

  • 0.96

  • 1.75

  • 0.16

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51 mark

This question relates to the equilibrium gas-phase synthesis of methanol:

CO (g) + 2H2 (g) ⇋ CH3OH (g)

Thermodynamic data for the components of this equilibrium are:

Substance

CO (g)

H2 (g)

CH3OH (g)

ΔHfӨ / kJ mol-1

-110

0

-201

SӨ / J K-1 mol-1

198

131

240

 

This equilibrium occurs at a temperature of 585 K, a total pressure of 45.0 MPa and in a 1.80 dm3 vessel.

At equilibrium, the vessel contains 0.0400 mol of CO (g), 0.0800 mol of H2 (g) and 0.0450 mol of CH3OH (g).

With pressures expressed in MPa units, the numerical value of the equilibrium constant, Kp, is

  • 0.0517

  • 0.0868

  • 4.80

  • 0.00237

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