DP Chemistry (last assessment 2024)

Question 19M.1.sl.TZ2.13

Date	May 2019	Marks available	[Maximum mark: 1]	Reference code	19M.1.sl.TZ2.13
Level	sl	Paper	1	Time zone	TZ2
Command term		Question number	13	Adapted from	N/A

13.

[Maximum mark: 1]

19M.1.sl.TZ2.13

Consider the following equations.

2Al (s) + $\frac{3}{2}$ O₂ (g) → Al₂O₃ (s) ΔH^Ɵ = −1670 kJ
Mn (s) + O₂ (g) → MnO₂ (s) ΔH^Ɵ = −520 kJ

What is the standard enthalpy change, in kJ, of the reaction below?

4Al (s) + 3MnO₂ (s) → 2Al₂O₃ (s) + 3Mn (s)

A. −1670 + 520

B. $\frac{3}{2}$ (−1670) + 3(520)

C. 2(−1670) + 3(−520)

D. 2(−1670) + 3(520)

[1]

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It is pleasing that 83 % of the candidates were confident in applying Hess’s law to obtain an expression for the standard enthalpy change of reaction. The most commonly chosen distractor (C) had the correct coefficients but one of the signs was incorrect.

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Core

Core » Topic 5: Energetics/thermochemistry » 5.2 Hess’s Law

Core » Topic 5: Energetics/thermochemistry

Question 19M.1.sl.TZ2.13

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