DP Chemistry (first assessment 2025)

Test builder »

Question 21N.1A.HL.TZ0.15

Date	November 2021	Marks available	[Maximum mark: 1]	Reference code	21N.1A.HL.TZ0.15
Level	HL	Paper	1A	Time zone	TZ0
Command term	State	Question number	15	Adapted from	N/A

15.

[Maximum mark: 1]

21N.1A.HL.TZ0.15

Which equation represents the standard enthalpy of formation of lithium oxide?

A. 4Li (s) + O₂(g) → 2Li₂O (s)

B. 2Li (s) + $\frac{1}{2}$ O₂(g) → Li₂O (s)

C. Li (s) + $\frac{1}{4}$ O₂(g) → $\frac{1}{2}$ Li₂O (s)

D. Li (g) + $\frac{1}{4}$ O₂(g) → $\frac{1}{2}$ Li₂O (g)

[1]

Markscheme

B

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