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Date May 2021 Marks available 1 Reference code 21M.2.sl.TZ1.6
Level SL Paper 2 Time zone TZ1
Command term Outline Question number 6 Adapted from N/A

Question

When dinitrogen pentoxide, N2O5, is heated the colourless gas undergoes thermal decomposition to produce brown nitrogen dioxide:

N2O5 (g) → 2NO2 (g) + 12O2 (g)

Data for the decomposition at constant temperature is given.

Suggest how the extent of decomposition could be measured.

[1]
a.

Plot the missing point on the graph and draw the best-fit line.

[2]
b(i).

Deduce the relationship between the concentration of N2O5 and the rate of reaction.

[1]
b(ii).

Outline why increasing the concentration of N2O5 increases the rate of reaction.

[1]
b(iii).

Markscheme

use colorimeter
OR
change in colour
OR
change in volume
OR
change in pressure ✔

Accept suitable instruments, e.g. pressure probe/oxygen sensor.

a.

point correct ✔

straight line passing close to all points AND through origin ✔


Accept free hand drawn line as long as attempt to be linear and meets criteria for M2.

b(i).

« rate of reaction is directly» proportional to/∝[N2O5]
OR
doubling concentration doubles rate ✔


Do not accept “rate increases as concentration increases”/ positive correlation

Accept linear

b(ii).

greater frequency of collisions «as concentration increases»
OR
more collisions per unit time «as concentration increases» ✔


Accept “rate/chance/probability/likelihood” instead of “frequency”.

Do not accept just “more collisions”.

b(iii).

Examiners report

[N/A]
a.
[N/A]
b(i).
[N/A]
b(ii).
[N/A]
b(iii).

Syllabus sections

Core » Topic 6: Chemical kinetics » 6.1 Collision theory and rates of reaction
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