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3.Tetrafluoroethene, C2F4, is obtained from chlorodifluoromethane, CHClF2, according to the equation:

2CHClF2(g) C2F4(g) + 2HCl(g)             

(a)A 1.0 mol sample of CHClF2 is placed in a container of volume 18.5 dm3 and heated.

When equilibrium is reached, the mixture contains 0.20 mol of CHClF2

(i)Calculate the number of moles of C2F4 and the number of moles of HCl present at equilibrium.

Number of moles of C2F4 ...................................................................

Number of moles of HCl .....................................................................

(ii)Write an expression for Kc for the equilibrium.

........................................................................................…...............................

(iii)Calculate a value for Kc and give its units.

Calculation .......................................................................................................

........................................................................................…...............................

........................................................................................…...............................

........................................................................................…...............................

Units .................................................................................................................

(6)

(b)(i)State how the temperature should be changed at constant pressure to increase the equilibrium yield of C2F4

........................................................................................…...............................

(ii)State how the total pressure should be changed at constant temperature to increase the equilibrium yield of C2F4

........................................................................................…...............................

(2)

(Total 8 marks)

4

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