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Topic 17: Equilibrium
For HL students only
1. [1 mark]
For the reaction I2 (g) + 3Cl2 (g) ⇌ 2ICl3 (g) at a certain temperature, the equilibrium concentrations are (in mol dm−3):
[I2] = 0.20, [Cl2] = 0.20, [ICl3] = 2.0
What is the value of Kc?
A. 0.25
B. 50
C. 2500
D. 5000
2. [1 mark]
The graph shows Gibbs free energy of a mixture of N2O4 (g) and NO2 (g) in different proportions.
N2O4 (g) ⇌ 2NO2 (g)
Which point shows the system at equilibrium?
3. [1 mark]
1.0 mol each of sulfur dioxide, oxygen, and sulfur trioxide are in equilibrium.
2SO2 g+O2 g⇌2SO3 g
Which change in the molar ratio of reactants will cause the greatest increase in the amount of sulfur trioxide?
Assume volume and temperature of the reaction mixture remain constant.
4a. [2 marks]
Hydrogen peroxide can react with methane and oxygen to form methanol. This reaction can occur below 50°C if a gold nanoparticle catalyst is used.
The diagram shows the Maxwell-Boltzmann curve for the uncatalyzed reaction.
Draw a distribution curve at a lower temperature (T2) and show on the diagram how the addition of a catalyst enables the reaction to take place more rapidly than at T1.
4b. [1 mark]
The hydrogen peroxide could cause further oxidation of the methanol. Suggest a possible oxidation product.
4c. [1 mark]
Methanol is usually manufactured from methane in a two-stage process.
CH4 (g) + H2O (g) ⇌ CO (g) + 3H2 (g)
CO (g) + 2H2 (g) ⇌ CH3OH (l)
CO (g) + 2H2 (g) ⇌ CH3OH (l)
Determine the overall equation for the production of methanol.
4d. [3 marks]
8.00 g of methane is completely converted to methanol. Calculate, to three significant figures, the final volume of hydrogen at STP, in dm3. Use sections 2 and 6 of the data booklet.
4e. [3 marks]
Consider the first stage of the reaction.
CH4 (g) + H2O (g) ⇌ CO (g) + 3H2 (g)
Determine the enthalpy change, ΔH, in kJ. Use section 11 of the data booklet.
Bond enthalpy of CO = 1077 kJ mol−1.
4f. [1 mark]
State one reason why you would expect the value of ΔH calculated from the Hf values, given in section 12 of data booklet, to differ from your answer to (d)(i).
4g. [1 mark]
State the expression for Kc for this stage of the reaction.
4h. [1 mark]
State and explain the effect of increasing temperature on the value of Kc.
4i. [2 marks]
Hydrogen peroxide can react with methane and oxygen to form methanol. This reaction can occur below 50°C if a gold nanoparticle catalyst is used.
Now consider the second stage of the reaction.
CO (g) + 2H2 (g) ⇌ CH3OH (l) ΔH⦵ = –129 kJ
The equilibrium constant, Kc, has a value of 1.01 at 298 K.
Calculate ΔG⦵, in kJ mol–1, for this reaction. Use sections 1 and 2 of the data booklet.
4j. [2 marks]
Calculate a value for the entropy change, ΔS⦵, in J K–1 mol–1 at 298 K. Use your answers to (e)(i) and section 1 of the data booklet.
If you did not get answers to (e)(i) use –1 kJ, but this is not the correct answer.
4k. [1 mark]
Justify the sign of ΔS with reference to the equation.
4l. [1 mark]
Predict, giving a reason, how a change in temperature from 298 K to 273 K would affect the spontaneity of the reaction.
5a. [1 mark]
Consider the following equilibrium reaction:
2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
State the equilibrium constant expression, Kc, for the reaction above.
5b. [3 marks]
State and explain how the equilibrium would be affected by increasing the volume of the reaction container at a constant temperature.
6. [1 mark]
Which is correct for a reaction with a positive change in Gibbs free energy, ΔGθ?
A. The formation of reactants is favoured.
B. The formation of products is favoured.
C. The reaction is at equilibrium.
D. The reaction is spontaneous.
7. [1 mark]
Iodine and bromine gases were mixed and allowed to reach equilibrium.
What is the value of the equilibrium constant?
A. 0.05
B. 1
C. 4
D. 10
8. [1 mark]
Which combination describes the system at equilibrium?
9a. [1 mark]
This reaction is used in the manufacture of sulfuric acid.
2SO2 (g) + O2 (g) ⇌ 2SO3 (g) Kc = 280 at 1000 K
State why this equilibrium reaction is considered homogeneous.
9b. [1 mark]
Predict, giving your reason, the sign of the standard entropy change of the forward reaction.
9c. [2 marks]
Calculate the standard Gibbs free energy change, ΔGΘ, in kJ, for this reaction at 1000 K. Use sections 1 and 2 of the data booklet.
9d. [2 marks]
Predict, giving your reasons, whether the forward reaction is endothermic or exothermic. Use your answers to (b) and (c).
9e. [3 marks]
0.200 mol sulfur dioxide, 0.300 mol oxygen and 0.500 mol sulfur trioxide were mixed in a 1.00 dm3 flask at 1000 K.
Predict the direction of the reaction showing your working.
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