DP Chemistry (last assessment 2024)

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Question 22N.2.hl.TZ0.f.iv

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Date November 2022 Marks available [Maximum mark: 2] Reference code 22N.2.hl.TZ0.f.iv
Level hl Paper 2 Time zone TZ0
Command term Justify, Predict Question number f.iv Adapted from N/A
f.iv.
[Maximum mark: 2]
22N.2.hl.TZ0.f.iv

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

Solid ammonium nitrate can decompose to gaseous dinitrogen monoxide and liquid water.

Predict, with a reason, the signs for the entropy change, ΔS⦵, and Gibbs free energy change, ΔG⦵, of the reaction.

 

[2]

Markscheme

Entropy change:

positive AND formation of gas «and liquid from solid» ✔

 

Gibbs free energy change:

negative AND increase in entropy/ΔS positive AND exothermic reaction/ΔH negative ✔

Examiners report

Candidates gained on average just half marks and the mark obtained seemed to correlate closely to their performance on the rest of the paper. Most candidates managed to predict that the formation of a gas resulted in an entropy increase, though a handful only mentioned the number of moles of product rather than noting their states. Slightly fewer were able deduce that the signs of the entropy and enthalpy changes meant that the reaction would be spontaneous at all temperatures.

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