DP Chemistry (last assessment 2024)
Question 21M.2.sl.TZ2.b
| Date | May 2021 | Marks available | [Maximum mark: 2] | Reference code | 21M.2.sl.TZ2.b |
| Level | sl | Paper | 2 | Time zone | TZ2 |
| Command term | Calculate | Question number | b | Adapted from | N/A |
b.
[Maximum mark: 2]
21M.2.sl.TZ2.b
Limestone can be converted into a variety of useful commercial products through the lime cycle. Limestone contains high percentages of calcium carbonate, CaCO3.
Thermodynamic data for the decomposition of calcium carbonate is given.
Calculate the enthalpy change of reaction, ΔH, in kJ, for the decomposition of calcium carbonate.
[2]
Markscheme
«ΔH =» (−635 «kJ» – 393.5 «kJ») – (−1207 «kJ») ✓
«ΔH = + » 179 «kJ» ✓
Award [2] for correct final answer.
Award [1 max] for −179 kJ.
Ignore an extra step to determine total enthalpy change in kJ: 179 kJ mol−1 x 5.55 mol = 993 kJ.
Award [2] for an answer in the range 990 - 993« kJ».
