DP Chemistry (last assessment 2024)

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

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

[Maximum mark: 2]

20N.2.sl.TZ0.3b

An equation for the combustion of propane is given below.

C₃H₈(g) + 5O₂(g) 3CO₂(g) + 4H₂O(g)

(b)

Calculate the standard enthalpy change, $∆ H^{⦵}$ , for this reaction using section 12 of the data booklet.

[2]

Markscheme

$4 (- 241.8 « kJ »)$ AND $3 (- 393.5 « kJ »)$ AND $« 1 » (- 105 « kJ »)$ ✔

$« {ΔH}^{⦵} = 4 (- 241.8 « kJ ») + 3 (- 393.5 « kJ ») - « 1 » (- 105 « kJ ») = » - 2043 « kJ »$ ✔

Award [2] for correct final answer.

Award [1 max] for $- 2219 « k J »$ .

Examiners report

About half of the candidates obtained both marks. In the incorrect answers coefficients were sometimes ignored, some candidates used the wrong state for water, and some candidates did not realize the heat of formation of O₂ was zero and inserted the bond enthalpy for O₂ in the calculation.

Syllabus sections

Core

Core » Topic 5: Energetics/thermochemistry » 5.3 Bond enthalpies

Core » Topic 5: Energetics/thermochemistry

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

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