DP Chemistry (last assessment 2024)

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Question 22M.2.hl.TZ2.8f(i)

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Date May 2022 Marks available [Maximum mark: 3] Reference code 22M.2.hl.TZ2.8f(i)
Level hl Paper 2 Time zone TZ2
Command term Calculate Question number f(i) Adapted from N/A
f(i).
[Maximum mark: 3]
22M.2.hl.TZ2.8f(i)

Carbon forms many compounds.

Chlorine reacts with methane.

CH4 (g) + Cl2 (g) → CH3Cl (g) + HCl (g)

(f(i))

Calculate the enthalpy change of the reaction, ΔH, using section 11 of the data booklet.

[3]

Markscheme

bond breaking: C–H + Cl–Cl / 414 «kJ mol–1» + 242 «kJ mol–1»/656 «kJ»
OR
bond breaking: 4C–H + Cl–Cl / 4 × 414 «kJ mol–1» + 242 «kJ mol–1» / 1898 «kJ» ✔

 

bond forming: «C–Cl + H–Cl / 324 kJ mol–1 + 431 kJ mol–1» / 755 «kJ»
OR
bond forming: «3C–H + C–Cl + H–Cl / 3 × 414 «kJ mol–1» + 324 «kJ mol–1» + 431 kJ mol–1» / 1997 «kJ» ✔

 

«ΔH = bond breaking – bond forming = 656 kJ – 755 kJ» = –99 «kJ» ✔

 

Award [3] for correct final answer.

Award [2 max] for 99 «kJ».

Examiners report

Only the very weak candidates were unable to calculate the enthalpy change correctly, eventually missing 1 mark for inverted calculations.

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