DP Chemistry (last assessment 2024)

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Question 21M.2.hl.TZ1.4e(ii)

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Date May 2021 Marks available [Maximum mark: 2] Reference code 21M.2.hl.TZ1.4e(ii)
Level hl Paper 2 Time zone TZ1
Command term Calculate Question number e(ii) Adapted from N/A
e(ii).
[Maximum mark: 2]
21M.2.hl.TZ1.4e(ii)

Hydrogen peroxide can react with methane and oxygen to form methanol. This reaction can occur below 50°C if a gold nanoparticle catalyst is used.

Now consider the second stage of the reaction.

CO (g) + 2H2 (g) ⇌ CH3OH (l)          ΔH⦵ = –129 kJ

(e(ii))

Calculate a value for the entropy change, ΔS⦵, in J K–1 mol–1 at 298 K. Use your answers to (e)(i) and section 1 of the data booklet.

If you did not get answers to (e)(i) use –1 kJ, but this is not the correct answer.

[2]

Markscheme

«ΔG⦵ = ΔH⦵ − TΔS⦵»

ΔG⦵ = −129 «kJ mol–1» − (298 «K» × ΔS) = −0.0246 «kJ mol–1» ✔

ΔS⦵ = « 129 kJ mol-1+0.0246 kJ mol-1×103298 K = » −433 «J K–1 mol–1» ✔


Award [2] for correct final answer.

Award [1 max] for “−0.433 «kJ K–1 mol–1»”.

Award [1 max] for “433” or “+433” «J K–1 mol–1».

Award [2] for −430 «J K–1 mol–1» (result from given values).

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