1) The reaction between iron(III) ions, Fe³⁺(aq), and thiocyanate ions, SCN^- (aq), produces iron(III) thiocyanate ions, FeSCN²⁺(aq).

A few drops of sodium thiocyanate solution, NaSCN(aq), are added to 200 ml of the equilibrium mixture at constant temperature.
The concentration-time graph shows the change in concentration of SCN-(aq).

Which one of the following statements is true?
A. The equilibrium constant at t4 is lower than at t1 .
B. The chemical energy of the system increases between t3 and t4 .
C. The rate of the reverse reaction is less than the rate of the forward reaction at t3 .
D. Both the concentrations of Fe³⁺ and FeSCN²⁺ are higher at t3 than at t1.

Solution

4) Ammonia gas, NH₃(g), can be made by reacting a mixture of nitrogen gas, N₂(g), and hydrogen gas, H₃(g), using an iron catalyst.
The reaction can be represented by the equation

The equilibrium constant, KP, at 400 °C is 1.60 x 10^-8 kPa^-2.
In a mixture that is at equilibrium at 400 °C, the partial pressure of H₂ is 88.7 kPa and the partial pressure of N₂ is 43.4 kPa.


I

Explain how the iron catalyst addresses the conflict between optimal rate and temperature considerations in the production of NH₃ Support your answer with reference to one green chemistry principle. Refer to item 26.ii of the Data Book. 3 marks

Solution