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CHEMISTRY, M5 2020 HSC 26

Nitric oxide gas (`text{NO}`) can be produced from the direct combination of nitrogen gas and oxygen gas in a reversible reaction.

  1. Write the balanced chemical equation for this reaction.   (1 mark)

  2. The energy profile diagram for this reaction is shown. 
     

   

  1. Explain, using collision theory, how an increase in temperature would affect the value of `K_{eq}` for this system. Refer to the diagram in your answer.   (4 marks)

Show Answers Only

a.   \(\ce{N2(g) + O2(g) \rightleftharpoons 2NO(g) }\)
 

b.    Increased temperature’s effect on `K_{eq}`:

  • From the graph, the forward reaction is endothermic.
  • The activation energy of the forward endothermic reaction is greater than the activation energy of the reverse exothermic reaction.
  • An increase in temperature would cause the rates of both the forward and reverse reaction due to the higher average kinetic energy, resulting in a larger likelihood of a successful collisions.
  • However, the rate of the forward reaction would increase to a higher extent than the reverse reaction, since it is an endothermic reaction.
  • Using  `K_(eq) = ([text{NO}]^2)/([text{N}_2][text{O}_2])`, as the equilibrium shifts right, the equilibrium constant would increase.
Show Worked Solution

a.   \(\ce{N2(g) + O2(g) \rightleftharpoons 2NO(g) }\)
 

b.    Increased temperature’s effect on `K_{eq}`:

  • From the graph, the forward reaction is endothermic.
  • The activation energy of the forward endothermic reaction is greater than the activation energy of the reverse exothermic reaction.
  • An increase in temperature would cause the rates of both the forward and reverse reaction due to the higher average kinetic energy, resulting in a larger likelihood of a successful collisions.
  • However, the rate of the forward reaction would increase to a higher extent than the reverse reaction, since it is an endothermic reaction.
  • Using  `K_(eq) = ([text{NO}]^2)/([text{N}_2][text{O}_2])`, as the equilibrium shifts right, the equilibrium constant would increase.