(a) List three properties of a system that is in a state of chemical equilibrium.
(b) Consider reaction represented by the following equation: 3H\(_{2(g)}\) + N\(_{2(g)}\) \(\rightleftharpoons\) 2NH\(_{3(g)}\); H = 92KJ
(i) Explain the effect of increasing the temperature of the reaction on the yield of ammonia
(ii) Uses of energy profile diagram to illustrate the effect of a positive catalyst on the rate of either the forward reaction or the reverse reaction.
(c) In the extraction of aluminium from bauxite:
(i) outline the procedure used for purifying the ore;
(ii) write equation for the reaction at each electrode, during the electrolysis of the pure alumina;
(iii) state the function of molten cryolite in the electrolytic cell for the extraction.
Explanation
(a) The three properties are:-
(i) The reaction occurring in the system is reversible.
(ii) the rate of the forward reaction is equal to that of the reverse reaction
(iii) The value of the free energy change of the system is zero
(b)(i) Since the forward reaction is exothermic, increase in temperature will not favour the forward reaction. The yield of ammonia will be lower.
(c)(i) The ore is powdered and dissolved under pressure in a hot concentrated solution of sodium hydroxide. Sodium aluminate solution is formed Al\(_2\)O\(_3\) + 2NaOH \(\to\) 2NaAIO\(_2\) + H\(_2\)O. The impurities do not dissolve and filtered off. The sodium aluminium hydroxide to precipitate the hydroxide which is filtered off, washed, dried and heated strongly to form pure alumina.
2A1(OH)\(_3\) \(\to\) Al\(_2\)O\(_3\) + 3H\(_2\)O
Al\(_2\)O\(_{3(s)}\) + 2NaOH\(_{(aq)}\) + 3H\(_2\)O --> 2NaAl(OH)\(_4\)
Then; NaAI(OH)\(_{4(aq)}\) --> Al(OH)\(_{3(s)}\) + NaOH\(_{(aq)}\)
(ii) At the ANODE: 2O\(^{2-}\) - 4e\(^-\) \(\to\) O\(_2\) OR 2O\(^{2-}\) ---> O\(_2\) + 4e\(^-\)
At the CATHODE: Al\(^{3+}\) + 3e\(^-\) -> Al
(iii) The function is to act as a solvent or as a flux.