DP Chemistry (first assessment 2025)

Test builder »

Question 22M.2.SL.TZ1.3b(i)

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

Good performance; often the bond energy for single N–N bond instead of using it for the triple bond and not taking into consideration the coefficient of three in calculation of bond enthalpies of ammonia. Also, instead of using BE of bonds broken minus those that were formed, the operation was often reversed. Students should be encouraged to draw the Lewis structures in the equations first to determine the bonds being broken and formed.

Syllabus sections