Question 22M.2.sl.TZ2.3a
| Date | May 2022 | Marks available | [Maximum mark: 2] | Reference code | 22M.2.sl.TZ2.3a |
| Level | sl | Paper | 2 | Time zone | TZ2 |
| Command term | Justify, Outline | Question number | a | Adapted from | N/A |
Sulfur trioxide is produced from sulfur dioxide.
2SO2 (g) + O2 (g) 2SO3 (g) ΔH = −196 kJ mol−1
Outline, giving a reason, the effect of a catalyst on a reaction.
[2]
increases rate AND lower Ea ✔
provides alternative pathway «with lower Ea»
OR
more/larger fraction of molecules have the «lower» Ea ✔
Accept description of how catalyst lowers Ea for M2 (e.g. “reactants adsorb on surface «of catalyst»”, “reactant bonds weaken «when adsorbed»”, “helps favorable orientation of molecules”).
A generally well-answered question. Most candidates explained the effect of a catalyst on a reaction correctly. A small proportion of candidates thought the catalyst increased the frequency of collisions. Some candidates focussed on the effect of the catalyst on an equilibrium since the equation above the question was that of a reversible reaction. These candidates usually still managed to gain at least the first marking point by stating that both forward and reverse reaction rates were increased due to the lower activation energy. Most candidates mentioned the alternative pathway for the second mark, and some gave a good discussion about the increase in the number of molecules or collisions with E≥Ea. A few candidates lost one of the marks for not explicitly stating the effect of a catalyst (that it increases the rate of the reaction).
