Question 23M.2.SL.TZ2.2
| Date | May 2023 | Marks available | [Maximum mark: 7] | Reference code | 23M.2.SL.TZ2.2 |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Calculate, Deduce, Outline, Predict, Suggest, Write | Question number | 2 | Adapted from | N/A |
Nitrogen (IV) oxide, NO2, is a brown gas found in photochemical smog and has a pollutant causing acid deposition.
Nitrogen (IV) oxide exists in equilibrium with dinitrogen tetroxide, N2O4 (g), which is colourless.
2NO2 (g) ⇌ N2O4 (g)
At 100 °C Kc for this reaction is 0.0665. Outline what this indicates about the extent of this reaction.
[1]
reaction hardly proceeds
OR
reverse reaction/formation of NO2 is favoured
OR
«concentration of» reactants greater than «concentration of» products «at equilibrium» ✓
Accept equilibrium lies to the left.
Calculate the value of Kc at 100 °C for the equilibrium:
N2O4 (g) ⇌ 2NO2 (g)
[1]
«Kc = =» 15.0 ✓
Calculate the standard enthalpy change, in kJ mol−1, for the reaction:
N2O4 (g) → 2NO2 (g)
| ΔH⦵f (kJ mol−1) | |
| NO2 |
33.18 |
| N2O4 |
9.16 |
[1]
« ΔH⦵ = 2(33.18) − 9.16 =» «+» 57.20 «kJ mol−1» ✓
Deduce the Lewis structure of N2O4.
[1]
Accept any combination of dots, crosses or lines to represent electron pairs.
The NO bond lengths in N2O4 are all 1.19 × 10−10m.
Suggest what the bond lengths indicate about the structure of N2O4.
[1]
it has resonance structures ✓
Accept bond order = 1.5.
Accept delocalized electrons «in NO bonds».
Predict the ONN bond angle in N2O4.
[1]
110–120° ✓
Accept any value in the range given.
(Bond angle is actually 112.3°.)
Acid deposition is formed when nitrogen oxides dissolve in water. Write an equation for nitrogen (IV) oxide reacting with water to produce two acids.
[1]
2NO2 (g) + H2O (l) → HNO2 (aq) + HNO3 (aq) ✓
Accept N2O4 (g) + H2O (l) → HNO2 (aq) + HNO3 (aq)