DP Chemistry (first assessment 2025)

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Question 21M.1A.HL.TZ2.17

Date	May 2021	Marks available	[Maximum mark: 1]	Reference code	21M.1A.HL.TZ2.17
Level	HL	Paper	1A	Time zone	TZ2
Command term	Predict	Question number	17	Adapted from	N/A

17.

[Maximum mark: 1]

21M.1A.HL.TZ2.17

Which change results in the largest negative value of ΔS?

A. C₂H₅OH (l) + SOCl₂(l) → C₂H₅Cl (l) + SO₂(g) + HCl (g)

B. CaCO₃(s) → CaO (s) + CO₂(g)

C. H₂O (l) → H₂O (s)

D. NH₃(g) + HCl (g) → NH₄Cl (s)

[1]

Markscheme

D

Syllabus sections

Reactivity 1. What drives chemical reactions? » Reactivity 1.4—Entropy and spontaneity (Additional higher level) » Reactivity 1.4.1—Entropy, S, is a measure of the dispersal or distribution of matter and/or energy in a system. The more ways the energy can be distributed, the higher the entropy. Under the same conditions, the entropy of a gas is greater than that of a liquid, which in turn is greater than that of a solid. Predict whether a physical or chemical change will result in an increase or decrease in entropy of a system. Calculate standard entropy changes, ΔS⦵, from standard entropy values, S⦵.