DP Chemistry (first assessment 2025)
Question 21M.2.HL.TZ2.1b(iii)
| Date | May 2021 | Marks available | [Maximum mark: 2] | Reference code | 21M.2.HL.TZ2.1b(iii) |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Determine | Question number | b(iii) | Adapted from | N/A |
b(iii).
[Maximum mark: 2]
21M.2.HL.TZ2.1b(iii)
(b(iii))
Determine the temperature, in K, at which the decomposition of calcium carbonate becomes spontaneous, using b(i), b(ii) and section 1 of the data booklet.
(If you do not have answers for b(i) and b(ii), use ΔH = 190 kJ and ΔS = 180 J K−1, but these are not the correct answers.)
[2]
Markscheme
«spontaneous» if ΔG = ΔH − TΔS < 0
OR
ΔH < TΔS ✓
«T >=» 1112 «K» ✓
Award [2] for correct final answer.
Accept “1056 K” if both of the incorrect values are used to solve the problem.
Do not award M2 for any negative T value.
Syllabus sections
Reactivity 1. What drives chemical reactions? » Reactivity 1.4—Entropy and spontaneity (Additional higher level) » Reactivity 1.4.2—Change in Gibbs energy, ΔG, relates the energy that can be obtained from a chemical reaction to the change in enthalpy, ΔH, change in entropy, ΔS, and absolute temperature, T. Apply the equation ΔG⦵ = ΔH⦵ − TΔS⦵ to calculate unknown values of these terms.