DP Chemistry (first assessment 2025)
Question 23M.2.HL.TZ2.9
| Date | May 2023 | Marks available | [Maximum mark: 4] | Reference code | 23M.2.HL.TZ2.9 |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Calculate, Deduce | Question number | 9 | Adapted from | N/A |
9.
[Maximum mark: 4]
23M.2.HL.TZ2.9
The initial rate of reaction was determined for the reaction between bromide ions, Br− (aq), and bromate ions, BrO3− (aq), in acidic solution.
5Br− (aq) + BrO3− (aq) + 6H+ (aq) → 3Br2 (aq) + 3H2O (l)
Four trials were carried out and the results are given in the following table.
| Experiment |
[BrO3−] (mol dm−3) |
[Br−] (mol dm−3) |
[H+] (mol dm−3) |
Initial rate (mol dm−3 s−1) |
| 1 | 0.050 | 0.250 | 0.300 | 2.13 × 10−6 |
| 2 | 0.050 | 0.250 | 0.600 | 8.60 × 10−6 |
| 3 | 0.100 | 0.250 | 0.600 | 17.2 × 10−6 |
| 4 | 0.050 | 0.500 | 0.300 | 4.26 × 10−6 |
(a)
Deduce the overall rate equation.
[2]
Markscheme
H+: second order
AND
BrO3−: first order
AND
Br−: first order ✓
«rate =» k[Br−][BrO3−][H+]2 ✓
Award [2] for correct rate equation.
(b)
The rate of a reaction at 50 °C is three times the rate at 25 °C. Calculate the activation energy, in kJ mol−1, for this reaction using sections 1 and 2 of the data booklet.
[2]
Markscheme
«ln »
ln ✓
« »
«Ea = » 35.1 «kJ mol−1 »✓
Award [2] for correct final answer.