DP Chemistry (first assessment 2025)

Question 19M.2.SL.TZ2.2f

Date	May 2019	Marks available	[Maximum mark: 2]	Reference code	19M.2.SL.TZ2.2f
Level	SL	Paper	2	Time zone	TZ2
Command term	Annotate, Outline	Question number	f	Adapted from	N/A

[Maximum mark: 2]

19M.2.SL.TZ2.2f

(f)

The graph below shows the Maxwell–Boltzmann distribution of molecular energies at a particular temperature.

The rate at which dinitrogen monoxide decomposes is significantly increased by a metal oxide catalyst.

Annotate and use the graph to outline why a catalyst has this effect.

[2]

Markscheme

catalysed and uncatalysed E_a marked on graph AND with the catalysed being at lower energy [✔]

«for catalysed reaction» greater proportion of/more molecules have E ≥ E_a / E > E_a
OR
«for catalysed reaction» greater area under curve to the right of the E_a [✔]

Note: Accept “more molecules have the activation energy”.

Examiners report

The graph was generally well done, but in quite a few cases, candidates did not mention that increase of rate in the catalyzed reaction was due to E (particles) > E_a or did so too vaguely.

Syllabus sections

Reactivity 2. How much, how fast and how far? » Reactivity 2.2—How fast? The rate of chemical change » Reactivity 2.2.4—Activation energy, Ea, is the minimum energy that colliding particles need for a successful collision leading to a reaction. Construct Maxwell–Boltzmann energy distribution curves to explain the effect of temperature on the probability of successful collisions.

Question 19M.2.SL.TZ2.2f

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