This was the least popular question among candidates. However, the few candidates that attempted it had good performance.
In(a), candidates showed good mastery of the chemical equilibrium as they correctly stated the effect of each of the conditions on the equilibrium and condition for the attainment of a state of dynamic equilibrium respectively as follows :
(i)
I. equilibrium position shifts to the right
II. equilibrium position shifts to the right
III. equilibrium position shifts to the left
IV. equilibrium position shifts to the right
(ii) A reversible reaction is said to attain a state of equilibrium when the rate
of forward reaction is equal to the rate of the backward reaction.
In (b)(i), candidates correctly identified W, X, Y and Z as activation energy, activated complex, enthalpy change of reaction and reaction pathway/coordinate respectively.
In (b)(ii) and (iii), the candidates correctly stated that the reaction is endothermic because the heat content of the product is greater than that of the reactants and addition of a catalyst would reduce the value of W.
In (c)(i), only a few candidates could write the expected equation thus:
C(s) + O2(g) → CO2(g)
CO2(g) + C(s) → 2CO(g)
Fe2O3(s) + 3CO(g) → Fe(1) + 3CO2(g)
CaCO3(S) → CaO(S) + CO2(g)
SiO2(s) + CaO(s) → CaSiO3(1)
In (c)(ii) and (iii), candidates correctly stated three methods by which the reaction could be prevented (i.e.galvanization, painting, electroplating, greasing/oiling) and that the oxidation state of iron in the product is +3.
In (d)(i) and (ii), candidates did not know the reason why gases deviate from ideal gas behaviour nor the condition under which a gas behaves ideally.
The expected answers from candidates were:
(i) - existence of intermolecular forces of attraction between the molecules of the gases.
- volume possessed by molecules of gases is not negligible.
(ii) - at high temperature
- at low pressure.
In (d) (iii), most candidates were able to correctly draw a sketch to illustrate Boyle’s law 
