User interface language: English | Español

Date May 2017 Marks available 2 Reference code 17M.2.hl.TZ2.9
Level HL Paper 2 Time zone TZ2
Command term Calculate Question number 9 Adapted from N/A

Question

The Bombardier beetle sprays a mixture of hydroquinone and hydrogen peroxide to fight off predators. The reaction equation to produce the spray can be written as:

C6H4(OH)2(aq) + H2O2(aq) C6H4O2(aq) + 2H2O(l)
hydroquinone   quinone


 

Hydrogenation of propene produces propane. Calculate the standard entropy change, ΔSθ, for the hydrogenation of propene.

[2]
b.i.

The standard enthalpy change, ΔH θ, for the hydrogenation of propene is –124.4 kJ mol–1. Predict the temperature above which the hydrogenation reaction is not spontaneous.

[2]
b.ii.

Markscheme

«ΔSθ =» 270 «J K–1 mol–1» – 267 «J K–1 mol–1» – 131 «J K–1 mol–1»

«ΔSθ =» –128 «J K–1 mol–1»

 

Award [2] for correct final answer.

[2 marks]

b.i.

«non spontaneous if» ΔG θ = ΔH θ – TΔS θ > 0
OR
ΔH θ > TΔS θ

«T above» 124.4   kJ mo l 1 0.128   kJ K 1 mo l 1 = » 972 «K»

 

Award [2] for correct final answer.

Accept 699 °C.

Do not award M2 for any negative T value.

[2 marks]

b.ii.

Examiners report

[N/A]
b.i.
[N/A]
b.ii.

Syllabus sections

Core » Topic 10: Organic chemistry » 10.1 Fundamentals of organic chemistry
Show 138 related questions
Additional higher level (AHL) » Topic 15: Energetics/thermochemistry » 15.2 Entropy and spontaneity
Additional higher level (AHL) » Topic 15: Energetics/thermochemistry
Core » Topic 10: Organic chemistry
Core
Additional higher level (AHL)

View options