DP Chemistry (last assessment 2024)

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Question 20N.2.hl.TZ0.a

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Date November 2020 Marks available [Maximum mark: 3] Reference code 20N.2.hl.TZ0.a
Level hl Paper 2 Time zone TZ0
Command term Determine Question number a Adapted from N/A
a.
[Maximum mark: 3]
20N.2.hl.TZ0.a

An equation for the combustion of propane is given below.

C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)

Determine the standard enthalpy change, ∆H⦵, for this reaction, using section 11 of the data booklet.

 

[3]

Markscheme

Bonds broken: 8(C–H) + 2(C–C) + 5(O=O) / 8 × 414 «kJ mol−1» + 2 × 346 «kJ mol−1» + 5 × 498 «kJ mol−1» / 6494 «kJ» ✔

Bonds formed: 6(C=O) + 8(O–H) / 6 × 804 «kJ mol−1» + 8 × 463 «kJ mol−1» / 8528 «kJ» ✔

«Enthalpy change=bonds broken-bonds formed =6494 kJ−8528 kJ=»−2034 «kJ»  ✔

Award [3] for correct final answer.

 

Examiners report

Many candidates had difficulty determining the number and type of bonds broken or formed and consequently this was the part of question 3 that was most poorly attempted. Those that could identify these bonds performed the calculations correctly.

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