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Question 19M.2.hl.TZ2.1c(ii)

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Date May 2019 Marks available [Maximum mark: 3] Reference code 19M.2.hl.TZ2.1c(ii)
Level hl Paper 2 Time zone TZ2
Command term Determine Question number c(ii) Adapted from N/A
c(ii).
[Maximum mark: 3]
19M.2.hl.TZ2.1c(ii)

Ethyne, C2H2, reacts with oxygen in welding torches.

Ethyne reacts with steam.

C2H2 (g) + H2O (g) → C2H4O (g)

Two possible products are:

(c(ii))

Determine the enthalpy change for the reaction, in kJ, to produce A using section 11 of the data booklet.

[3]

Markscheme

«sum of bond enthalpies of reactants =» 2(C—H)+C ≡ C + 2(O—H)
OR
2 × 414 «kJ mol-1» + 839 «kJ mol-1» + 2 × 463 «kJ mol-1»
OR
2593 «kJ»    [✔]

 

«sum of bond enthalpies of A =» 3(C—H) + C=C + C—O + O—H
OR
3 × 414 «kJ mol-1» + 614 «kJ mol-1» + 358 «kJ mol-1» + 463 «kJ mol-1»
OR
2677 «kJ»     [✔]
«enthalpy of reaction = 2593 kJ – 2677 kJ» = –84 «kJ»     [✔]

 

Note: Award [3] for correct final answer.

Examiners report

Candidates were able to calculate the ΔH of the given reaction correctly; a few inverted the calculations or made mathematical errors.

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