Question 18M.2.hl.TZ1.3
| Date | May 2018 | Marks available | [Maximum mark: 16] | Reference code | 18M.2.hl.TZ1.3 |
| Level | hl | Paper | 2 | Time zone | TZ1 |
| Command term | Calculate, Determine, Draw, Explain, Formulate, Justify, Outline, Show, State | Question number | 3 | Adapted from | N/A |
This question is about ethene, C2H4, and ethyne, C2H2.
Ethyne, like ethene, undergoes hydrogenation to form ethane. State the conditions required.
[2]
nickel/Ni «catalyst»
high pressure
OR
heat
Accept these other catalysts: Pt, Pd, Ir, Rh, Co, Ti.
Accept “high temperature” or a stated temperature such as “150 °C”.
[2 marks]
Outline the formation of polyethene from ethene by drawing three repeating units of the polymer.
[1]
Ignore square brackets and “n”.
Connecting line at end of carbons must be shown.
[1 mark]
Ethyne reacts with chlorine in a similar way to ethene. Formulate equations for the following reactions.
[2]
ethyne: C2H2 + Cl2 → CHClCHCl
benzene: C6H6 + Cl2 → C6H5Cl + HCl
Accept “C2H2Cl2”.
[2 marks]
Under certain conditions, ethyne can be converted to benzene.
Determine the standard enthalpy change, ΔHΘ, for the reaction stated, using section 11 of the data booklet.
3C2H2(g) → C6H6(g)
[2]
ΔHΘ = bonds broken – bonds formed
«ΔHΘ = 3(C≡C) – 6(C
C)benzene / 3 839 – 6 507 / 2517 – 3042 =» –525 «kJ»
Award [2] for correct final answer.
Award [1 max] for “+525 «kJ»”.
Award [1 max] for:
«ΔHΘ = 3(C≡C) – 3(C–C) – 3(C=C) / 3 839 – 3 346 – 3 614 / 2517 – 2880 =» –363 «kJ».
[2 marks]
Determine the standard enthalpy change, ΔHΘ, for the following similar reaction, using ΔHf values in section 12 of the data booklet.
3C2H2(g) → C6H6(l)
[2]
ΔHΘ = ΣΔHf (products) – ΣΔHf (reactants)
«ΔHΘ = 49 kJ – 3 228 kJ =» –635 «kJ»
Award [2] for correct final answer.
Award [1 max] for “+635 «kJ»”.
[2 marks]
Explain, giving two reasons, the difference in the values for (c)(i) and (ii). If you did not obtain answers, use −475 kJ for (i) and −600 kJ for (ii).
[2]
ΔHf values are specific to the compound
OR
bond enthalpy values are averages «from many different compounds»
condensation from gas to liquid is exothermic
Accept “benzene is in two different states «one liquid the other gas»” for M2.
[2 marks]
Calculate the standard entropy change, ΔSΘ, in J K−1, for the reaction in (ii) using section 12 of the data booklet.
[1]
«ΔSΘ = 173 – 3 201 =» –430 «J K–1»
[1 mark]
Determine, showing your working, the spontaneity of the reaction in (ii) at 25 °C.
[3]
T = «25 + 273 =» 298 «K»
ΔGϴ «= –635 kJ – 298 K × (–0.430 kJ K–1)» = –507 kJ
ΔGϴ < 0 AND spontaneous
ΔGϴ < 0 may be inferred from the calculation.
[3 marks]
One possible Lewis structure for benzene is shown.
State one piece of physical evidence that this structure is incorrect.
[1]
equal C–C bond «lengths/strengths»
OR
regular hexagon
OR
«all» C–C have bond order of 1.5
OR
«all» C–C intermediate between single and double bonds
Accept “all C–C–C bond angles are equal”.
[1 mark]