DP Chemistry (first assessment 2025)
Question 20N.2.HL.TZ0.7b
| Date | November 2020 | Marks available | [Maximum mark: 1] | Reference code | 20N.2.HL.TZ0.7b |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Deduce, Justify | Question number | b | Adapted from | N/A |
b.
[Maximum mark: 1]
20N.2.HL.TZ0.7b
(b)
Nitrogen monoxide reacts with oxygen gas to form nitrogen dioxide.
Deduce, giving a reason, whether the following mechanism is possible.
[1]
Markscheme
not possible AND «proposed» mechanism does not match experimental rate law
OR
not possible AND «proposed» mechanism shows zero/not first order with respect to oxygen ✔
Examiners report
60% of candidates could explain why the proposed reaction mechanism was inconsistent with the empirical data given.
Syllabus sections
Reactivity 2. How much, how fast and how far? » Reactivity 2.2—How fast? The rate of chemical change » Reactivity 2.2.6—Many reactions occur in a series of elementary steps. The slowest step determines the rate of the reaction. Evaluate proposed reaction mechanisms and recognize reaction intermediates. Distinguish between intermediates and transition states, and recognize both in energy profiles of reactions.