1.1. Dinitrogen tetraoxide, N₂O₄, is a colourless gas.

 Nitrogen dioxide, NO₂, is a brown gas.

The two gases can exist together in dynamic equilibrium according to the equation:

N₂O₄(g)    $\rightleftharpoons$     2NO₂(g)

Explain what is meant by the term dynamic equilibrium.

1.2. Some N₂O₄ and some NO₂ are put into a sealed gas syringe and allowed to form an equilibrium mixture. 

This equilibrium mixture is brown.

i) The pressure of the gas in the syringe is increased by pushing in the piston. The mixture is then allowed to reach a new equilibrium at the same temperature as before.

Explain why the new equilibrium mixture contains less NO₂ than the original equilibrium mixture.

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ii) A student suggests that the new equilibrium mixture would be lighter in colour than the original equilibrium mixture, as there is now less NO₂ present.

Suggest why the new equilibrium mixture is actually darker than the original.

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1.3. Carbon monoxide, CO, and oxides of nitrogen are produced in a car engine when petrol is burned.

These oxides can be partly removed by using a catalytic converter fitted to the car’s exhaust system.

i)State how oxides of nitrogen are produced in the car engine.

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ii) Give a disadvantage of allowing oxides of nitrogen to escape into the atmosphere.

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iii) Write a chemical equation for the reaction between nitrogen monoxide, NO, and carbon monoxide to form carbon dioxide and nitrogen.

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