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Question 20N.2.sl.TZ0.3a

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

An equation for the combustion of propane is given below.

C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)

(a)

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

This question was generally well answered. The mean mark on the question was 1.8 out of 3 marks. Mistakes included three C–C (instead of two), missing C–C bonds completely, subtracting bonds formed bonds broken, 3 and 4 instead of 6 and 8 for bonds formed coefficients, and bond enthalpies of C=O and O=O double bonds treated as single bonds.

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