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4.Nitrogen dioxide dissociates according to the following equation.

2NO2(g)  2NO(g)  +  O2(g)

When 21.3 g of nitrogen dioxide were heated to a constant temperature, T, in a flask of volume 11.5 dm3, an equilibrium mixture was formed which contained 7.04 g of oxygen.

(a)(i)Calculate the number of moles of oxygen present in this equilibrium mixture and deduce the number of moles of nitrogen monoxide also present in this equilibrium mixture.

Number of moles Of O2 at equilibrium ........................................................

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Number of moles of NO at equilibrium .......................................................

(ii)Calculate the number of moles in the original 21.3 g of nitrogen dioxide and hence calculate the number of moles of nitrogen dioxide present in this equilibrium mixture.

Original number of moles of NO2 ................................................................

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Number of moles of NO2 at equilibrium ......................................................

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(4)

(b)Write an expression for the equilibrium constant, Kc, for this reaction. Calculate the value of this constant at temperature T and give its units.

Expression for Kc ...................................................................................................

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

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(4)

(c)The total number of moles of gas in the flask is 0.683. Use the ideal gas equation to determine the temperature T at which the total pressure in the flask is 3.30 × 105 Pa. (The gas constant R = 8.31 J K–1mol–1)

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