DP Chemistry (last assessment 2024)

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Question 22N.2.hl.TZ0.1d.vi

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Date November 2022 Marks available [Maximum mark: 1] Reference code 22N.2.hl.TZ0.1d.vi
Level hl Paper 2 Time zone TZ0
Command term Calculate Question number d.vi Adapted from N/A
d.vi.
[Maximum mark: 1]
22N.2.hl.TZ0.1d.vi

Ammonium nitrate, NH4NO3, is used as a high nitrogen fertilizer.

Cold packs contain ammonium nitrate and water separated by a membrane.

(d.vi)

Calculate the standard Gibbs free energy change, ΔG⦵, in kJ mol−1, for the dissolution of ammonium nitrate at 298 K. Use sections 1 and 19 of the data booklet as well as your answer for question part (d)(v).

If you did not obtain an answer in (d)(v), use 102.3 J mol−1 K−1, although this is not the correct answer.

 

[1]

Markscheme

«ΔG°=ΔH°-TΔS°=25.69 kJ mol-1-298 K 108.7 J mol-1 K-1×1 kJ1000 J=

−6.70 «kJ mol−1» ✔

 

If 102.3 J mol−1 K−1 is used then answer is −4.80 KJ mol−1.

Examiners report

About 80% of students applied the appropriate equation to calculate the free energy change for the reaction from the entropy and enthalpy change values previously found. As might have been predicted quite a few candidates failed to convert the J of the previous calculation into kJ, and a handful left the temperature as Celsius.

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