Question 23M.2.SL.TZ1.2
| Date | May 2023 | Marks available | [Maximum mark: 17] | Reference code | 23M.2.SL.TZ1.2 |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Annotate, Deduce, Explain, Outline, Sketch, State, Suggest | Question number | 2 | Adapted from | N/A |
The periodic table is a useful tool in explaining trends of chemical behaviour.
Annotate and label the ground state orbital diagram of boron, using arrows to represent electrons.
[1]
arrows AND identifies 2s AND 2p sub orbitals ✓
Accept “hooks” to represent the electrons.
Sketch the shapes of the occupied orbitals identified in part (a)(i).
[2]
Px,y or z can be used.
M2 cannot be awarded if labels of orbital types are missing or incorrect
Node of p orbital must be at the origin
Explain the decrease in first ionization energy from Li to Cs, group 1.
[2]
valence electron further from nucleus/«atomic» radius larger «down the group» ✓
«electron» more shielded/ less attractive force/easier to remove ✓
State the electron domain geometry of the ammonia molecule.
[1]
tetrahedral ✓
Deduce the Lewis (electron dot) structure of ammonia and sketch its 3D molecular shape.
[2]
Accept a combination of dots /crosses /lines in the Lewis structure
Lone pair not required for shape
Explain, with reference to the forces between molecules, why ammonia has a higher boiling point than phosphine (PH3).
[3]
ammonia has intermolecular/IMF hydrogen bonds «phosphine does not» ✓
phosphine «and ammonia» dipole-dipole/London dispersion forces/instantaneous dipole attractions/Van der Waals forces ✓
hydrogen bonds stronger ✓
Accept converse argument.
Award 1 for stating that NH3 is more polar than phosphine so the dipole-dipole forces are stronger
Ammonia is manufactured by the Haber process.
N2 (g) + 3H2 (g) 2NH3 (g) = −92.0 kJ mol−1
Outline what is meant by dynamic equilibrium.
[1]
«in a closed system» the rate of the forward reaction equals the rate of the reverse reaction. ✓
Deduce the Kc expression for the reaction in part (d)(i).
[1]
[NH3]2/([N2][H2]3) ✓
The Haber process requires a catalyst. State how a catalyst functions.
[1]
alternate pathway AND lowers activation energy/Ea ✓
Sketch a Maxwell–Boltzmann distribution curve showing the activation energies with and without a catalyst.
[2]
correct shape curve starting at the origin, without touching the x axis at high energy. ✓
(Ea) catalysed <(Ea) uncatalysed on x axis. ✓
Ignore any shading under the curve.
Suggest how the progress of the reaction could be monitored.
[1]
change in AND
volume
OR
pressure
OR
temperature
OR
concentration of H2/N2/reactants/NH3 /product ✓
Do not accept pH.
Accept any valid method.