DP Chemistry (last assessment 2024)

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Question 22M.2.sl.TZ1.2d(i)

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Date May 2022 Marks available [Maximum mark: 3] Reference code 22M.2.sl.TZ1.2d(i)
Level sl Paper 2 Time zone TZ1
Command term Determine Question number d(i) Adapted from N/A
d(i).
[Maximum mark: 3]
22M.2.sl.TZ1.2d(i)

Ammonia, NH3, is industrially important for the manufacture of fertilizers, explosives and plastics.

The effect of temperature on the position of equilibrium depends on the enthalpy change of the reaction.

(d(i))

Determine the enthalpy change, ΔH, for the Haber–Bosch process, in kJ. Use Section 11 of the data booklet.

[3]

Markscheme

bonds broken: N≡N + 3(H–H) / «1 mol×»945 «kJ mol–1» + 3«mol»×436 «kJ mol–1» / 945 «kJ» + 1308 «kJ» / 2253 «kJ» ✔

bonds formed: 6(N–H) / 6«mol»×391 «kJ mol–1» / 2346 «kJ» ✔

ΔH = «2253 kJ – 2346 kJ = » –93 «kJ» ✔

 

Award [2 max] for (+)93 «kJ»

Examiners report

It was pleasing to see that about a third of students gaining full marks and an equal number only lost a single mark because they failed to locate the correct bond enthalpy for molecular nitrogen.

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