Question 19M.2.sl.TZ2.2c
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.sl.TZ2.2c |
| Level | sl | Paper | 2 | Time zone | TZ2 |
| Command term | Sketch | Question number | c | Adapted from | N/A |
The thermal decomposition of dinitrogen monoxide occurs according to the equation:
2N2O (g) → 2N2 (g) + O2 (g)
The reaction can be followed by measuring the change in total pressure, at constant temperature, with time.
The x-axis and y-axis are shown with arbitrary units.
The experiment is repeated using the same amount of dinitrogen monoxide in the same apparatus, but at a lower temperature.
Sketch, on the axes in question 2, the graph that you would expect.
[2]
smaller initial gradient [✔]
initial pressure is lower AND final pressure of gas lower «by similar factor» [✔]
This was a challenging question. Candidates usually obtained only one of the two marks allocated for the answer. Most of them scored the mark for a lower initial slope at low temperature, while others scored a mark for sketching their curve below the original curve as all pressures (initial and final) will be lower at the lower temperature. A teacher commented that the wording was unclear “sketch on the axes in question 2”, and it would have been better to label the graph instead.
