DP Chemistry (first assessment 2025)
Question 19M.2.SL.TZ2.c
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.SL.TZ2.c |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Explain | Question number | c | Adapted from | N/A |
c.
[Maximum mark: 2]
19M.2.SL.TZ2.c
Explain the action of metals as heterogeneous catalysts.
[2]
Markscheme
Any two of:
reactant(s) adsorb onto active sites/surface [✔]
bonds weakened/broken/stretched «in adsorbed reactants»
OR
activation energy lowered [✔]
products desorbed [✔]
Note: Accept “products released” for M3.
Examiners report
This question was reasonably answered with many candidates receiving a mark for the action of a catalyst. The terms adsorbed and desorbed were often missing.
Syllabus sections
Reactivity 2. How much, how fast and how far? » Reactivity 2.2—How fast? The rate of chemical change » Reactivity 2.2.5—Catalysts increase the rate of reaction by providing an alternative reaction pathway with lower Ea. Sketch and explain energy profiles with and without catalysts for endothermic and exothermic reactions. Construct Maxwell–Boltzmann energy distribution curves to explain the effect of different values for Ea on the probability of successful collisions.