DP Chemistry (first assessment 2025)

Question 20N.1A.SL.TZ0.13

Date	November 2020	Marks available	[Maximum mark: 1]	Reference code	20N.1A.SL.TZ0.13
Level	SL	Paper	1A	Time zone	TZ0
Command term	State	Question number	13	Adapted from	N/A

13.

[Maximum mark: 1]

20N.1A.SL.TZ0.13

Which equation shows the enthalpy of formation, $∆ H_{f}$ , of ethanol?

A. $2 C (s) + 3 H_{2} (g) + \frac{1}{2} O_{2} (g) \to C_{2} H_{5} OH (g)$

B. $4 C (s) + 6 H_{2} (g) + O_{2} (g) \to 2 C_{2} H_{5} OH (g)$

C. $2 C (s) + 3 H_{2} (g) + \frac{1}{2} O_{2} (g) \to C_{2} H_{5} OH (l)$

D. $4 C (s) + 6 H_{2} (g) + O_{2} (g) \to 2 C_{2} H_{5} OH (l)$

[1]

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Examiners report

Less than half of the candidates selected the correct equation for the enthalpy of formation of ethanol. The most common wrong answer involved ethanol formed as a gas.

Syllabus sections

Reactivity 1. What drives chemical reactions? » Reactivity 1.2—Energy cycles in reactions » Reactivity 1.2.4—An application of Hess’s law uses enthalpy of formation data or enthalpy of combustion data to calculate the enthalpy change of a reaction. Calculate enthalpy changes of a reaction using ΔHf⦵ data or ΔHc⦵ data: ΔH⦵ = Σ ΔHf⦵products − Σ ΔHf⦵reactants ΔH⦵ = Σ ΔHc, ⦵reactants − Σ ΔHc. ⦵products

Question 20N.1A.SL.TZ0.13

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