DP Chemistry (first assessment 2025)

Question 19M.1A.SL.TZ1.22

Date	May 2019	Marks available	[Maximum mark: 1]	Reference code	19M.1A.SL.TZ1.22
Level	SL	Paper	1A	Time zone	TZ1
Command term		Question number	22	Adapted from	N/A

22.

[Maximum mark: 1]

19M.1A.SL.TZ1.22

K_c for 2N₂O (g) $\rightleftharpoons$ 2N₂ (g) + O₂ (g) is 7.3 × 10³⁴.

What is K_c for the following reaction, at the same temperature?

N₂ (g) + $\frac{1}{2}$ O₂ (g) $\rightleftharpoons$ N₂O (g)

A. 7.3 × 10³⁴

B. $\frac{1}{{\sqrt {7.3 \times {{10}^{34}}} }}$

C. $\frac{1}{{7.3 \times {{10}^{34}}}}$

D. $\frac{1}{{2 \times 7.3 \times {{10}^{34}}}}$

[1]

Markscheme

Examiners report

Candidates scored well while one teacher thought it was a trick question and particularly tough. Relationship between K values on reversed equations should be understood.

Syllabus sections

Reactivity 2. How much, how fast and how far? » Reactivity 2.3—How far? The extent of chemical change » Reactivity 2.3.2—The equilibrium law describes how the equilibrium constant, K, can be determined from the stoichiometry of a reaction. Deduce the equilibrium constant expression from an equation for a homogeneous reaction.

Question 19M.1A.SL.TZ1.22

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