Question 19M.2.hl.TZ2.2b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.hl.TZ2.2b |
| Level | hl | Paper | 2 | Time zone | TZ2 |
| Command term | Outline | Question number | b | 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.
Outline, in terms of collision theory, how a decrease in pressure would affect the rate of reaction.
[2]
«rate of reaction decreases»
concentration/number of molecules in a given volume decreases
OR
more space between molecules [✔]
collision rate/frequency decreases
OR
fewer collisions per unit time [✔]
Note: Do not accept just “larger space/volume” for M1.
Few students were able to relate the effect of reduced pressure at constant volume with a decrease in concentration of gas molecules and mostly did not even refer to this, but rather concentrated on lower rate of reaction and frequency of collisions. Many candidates lost a mark by failing to explain rate as collisions per unit time, frequency, etc.
