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2001 Q28 (b) (4 marks)

 

Carbonyl chloride, COCl2, is a colourless, poisonous gas that is also known as phosgene. It is needed for the production of insecticides, polyurethane plastics and polycarbonate. It is produced from the exothermic equilibrium reaction of carbon monoxide gas and chlorine gas. When the reaction vessel if cooled below 8'C the phosgene is a liquid.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(i) Write a balanced equation for the formation of phosgene (2 marks)

 

(ii) Explain how industry could maximise the production of phosgene. (2 marks)

2003 - Q30 (d) (6 marks)

 

The Ostwald process is used for making nitric acid from ammonia, and involves several equilibrium steps.

 

(i) Identify the only factor that changes the value of an equilibrium constant. (1 mark)

 

(ii) One step in the process produces nitrogen dioxide according to the equation:

 

                                         2NO(g) + O2(g) <---> 2NO2(g).

 

This reaction is exothermic.

 

Describe TWO methods that could be used to increase the yield of nitrogen dioxide. (2 marks)

 

(iii) A 1 L reaction vessel initially contained 0.25 mol NO and 0.12 mol O2. After equilibrium was established there was only 0.05 mol NO.

 

Calculate the equilibrium constant for the reaction. Show all relevant working. (3 marks) 

2005 - Q28 (b) (6 marks)

 

Nitrogen dioxide forms an equilibrium mixture with dinitrogen tetraoxide as shown.

 

                                            2NO2(g) <---> N2O4(g)

 

At 100°C, K for this reaction is 2.08. At 25°C, a 1.00 L vessel initially contained 0.132 mol of NO2(g). Once equilibrium had been established, there was 0.0400 mol of N2O4(g) in the vessel.

 

(i) Explain the effects of the addition of a catalyst and an increase in pressure on the yield of N2O4 in this reaction when carried out at 25°C. (2 marks)

 

(ii) Calculate the equilibrium constant for this reaction at 25°C, and account for any difference from the K value at 100°C. (4 marks)

2007 - Q28 (c) (5 marks)

 

Hydrogen sulfide can be removed from natural gas via the following process.

 

        2H2S(g) + SO2(g)           3S(s) + 2H2O(g) ΔH = –145 kJ mol–1

 

(i) Write the equilibrium constant expression for this reaction. (1 mark)

 

(ii) Calculate the equilibrium constant, when 1.00 mol of H2S and 1.00 mol of SO2 react in a 1.00 L vessel at 373 K to give 0.50 mol of water vapour under equilibrium conditions. (2 marks)

 

(iii) Identify FOUR factors that would maximise the removal of H2S(g) in this reaction. (2 marks)

2002 - Q28 (b) (4 marks)

 

One of the reactions used to form sulfuric acid is the reaction of oxygen with sulfur dioxide under equilibrium conditions to form sulfur trioxide.

Before the reaction, the concentration of sulfur dioxide was 0.06 mol L−1 and the concentration of oxygen was 0.05 mol L−1 .

After equilibrium was reached, the concentration of sulfur trioxide was 0.04 mol L−1 .

 

Calculate the equilibrium constant, K, for the reaction. Show relevant working.

 

2002 - Q28 (d) (6 marks)

 

During your practical work, you performed a first-hand investigation involving an equilibrium reaction.

 

(i) Outline the procedure you used. (2 marks)

 

(ii) Explain how you analysed the equilibrium reaction qualitatively. ( 4 marks)

2008 - Q29 (c) (6 marks)

 

Consider the following mixture of gases in a closed 5.0 L vessel at 730°C.

 

    Gas                    Quantity (mol)

    CH4                           2.00

    H2O                           1.25

    CO                             0.75

    H2                             0.75

 

The following reaction occurs:

 

                  CH4 (g) + H2O(g) <---> CO(g) + 3H2 (g) ΔH = +206 kJ

 

The equilibrium constant, K, is 0.26 at 730°C.

 

(i) Determine whether the system is at equilibrium. (3 marks)

 

(ii) Explain how conditions in this reaction could be adjusted to increase the quantity of products. (3 marks)

2009 - Q27 (b) (6 marks)

 

At a particular temperature, iodine trichloride dissociates into iodine gas and chlorine gas according to the following equation:

 

                                2ICl3(g) <--->   I2(g) + 3Cl2(g) ΔH = 240 kJ

 

Initially 0.35 mol of ICl3(g) was introduced into a 1.0 L container and allowed to come to equilibrium. At equilibrium there was 0.45 mol L–1 of Cl2(g).

 

(i) Write the equilibrium constant expression for this reaction. (1 mark)

 

(ii) Calculate the value of K at this temperature. (3 marks)

 

(iii) What are TWO consequences of increasing the temperature of the mixture at equilibrium? (2 marks)

2010 - Q32 (c) (5 marks)

 

At room temperature 0.80 moles of SO2 and 0.40 moles of O2 were introduced into a sealed 10 L vessel and allowed to come to equilibrium.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(i) Write the equilibrium constant expression and calculate the value for the equilibrium constant at time A. (3 marks)

 

(ii) Explain why a new equilibrium position was established at time B. (2 marks)

2007 - Q28 (e) (6 marks)

 

You performed a first-hand investigation to model an equilibrium reaction. 

 

(i) Outline the procedure used and the results you obtained. (2 marks)

 

(ii) Identify a risk associated with this procedure. (1 mark)

 

(iii) Describe how this procedure models equilibrium and state a limitation of the model. (3 marks)

2011 - Q33 (a) (3 marks)

 

A student set up the following experiment to model a process and observed the colour change of the crystals.

 

 

 

 

 

 

 

 

 

Identify liquid X and explain the colour change of the crystals. Include a chemical equation in your answer.

2011 - Q33 (d) 5 marks)

 

(i) Models are often used to help explain complex concepts. Outline a first- hand investigation that can model an equilibrium reaction.  (2 marks)

 

(ii) Assess the validity of the information that could be collected in this investigation. (3 marks)

2012 - Q34 (b) (5 marks)

 

The equilibrium constant expression for a gaseous reaction is as follows:

 

 

 

 

 

 

 

 

(i) Write the equation for this reaction. (1 mark)

 

(ii) 0.400 moles of NO was placed in a 1.00 L vessel at 2000°C. The equilibrium concentration of N2 was found to be 0.198 mol L−1.

 

Calculate the equilibrium constant for this reaction and use this value to describe the position of the equilibrium. (3 marks)

 

(iii) What could be changed that would result in a different value of K for this equilibrium? (1 mark)

2014 - Q32 (b) (5 marks)

 

Nitrosyl chloride is introduced into an empty container. It then dissociates into nitric oxide and chlorine according to the equation:

 

                                           2NOCl(g)  <---->  2NO(g) + Cl2(g)

 

The reaction is endothermic.

 

(i) Explain the effect on the yield of NO(g) if the temperature is increased.

 

(ii) The equilibrium constant, K, for the reaction is 0.028.

 

Calculate the equilibrium concentration of NOCl(g) if the equilibrium concentration of Cl2(g) is 0.17 mol L−1.

2013 - Q32 (b) (5 marks)

 

Hydrogen iodide is a colourless gas that will decompose into colourless hydrogen gas and purple iodine gas according to the following endothermic reaction.

 

                                        2HI (g) <----> H2 (g) + I2 (g)

 

(i) A 1.0 L glass container was filled with 0.60 moles of hydrogen iodide gas. When equilibrium was established, there were 0.25 moles of iodine gas present in the container.

Calculate the equilibrium constant for this reaction.  (3 marks)

 

(ii) The container was then cooled. Explain the change in the appearance of its contents. (2 marks)

2015 - Q31 (a) (5 marks)

 

At temperatures above 100°C, hydrogen and carbon monoxide react to form methanol gas in this reversible reaction.

 

                                  2H2(g) + CO(g) <----> CH3OH(g)

 

A mixture of hydrogen, carbon monoxide and methanol is placed in a container with a volume that can be changed. The mixture is allowed to reach equilibrium.

 

(i) The initial volume of the container is 1.00 L.

 

Account for any changes in the concentration of hydrogen gas when the volume of the container is rapidly increased to 2.00 L. (2 marks)

 

(ii) The initial mixture placed in the container had 0.50 mol of hydrogen, 1.00 mol of carbon monoxide and 2.50 mol of methanol. Once the volume of the container had been increased to 2.00 L and equilibrium had been re-established, the number of moles of hydrogen in the mixture had changed by 0.36 mol.

 

Calculate the equilibrium constant for this reaction. (3 marks)

2016 - Q31 (c) (7 marks)

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(i) Methane and water vapour react to form carbon monoxide and hydrogen in a closed container as shown.

 

                    CH4(g) + H2O(g) <-----> CO(g) + 3H2(g)        ΔH = +206 kJ

 

Compare the impact on the equilibrium system of a decrease in volume of the container to the impact of a decrease in temperature. Refer to the equilibrium constant in your answer. (3 marks)

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(ii) Solid ammonium hydrogen sulfide (NH4HS) decomposes to form ammonia gas and hydrogen sulfide gas (H2S).

 

2.00 moles of ammonium hydrogen sulfide were placed in a sealed 3.00 L container and the system was allowed to reach equilibrium. At equilibrium, there were 0.0328 moles of ammonia gas.

 

Calculate the equilibrium constant for this reaction. (4 marks)

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