| Date | November 2017 | Marks available | 1 | Reference code | 17N.2.hl.TZ0.5 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Calculate | Question number | 5 | Adapted from | N/A |
Question
Ethane-1,2-diol, HOCH2CH2OH, reacts with thionyl chloride, SOCl2, according to the reaction below.
HOCH2CH2OH (l) + 2SOCl2 (l) → ClCH2CH2Cl (l) + 2SO2 (g) + 2HCl (g)
Calculate the standard enthalpy change for this reaction using the following data.
Calculate the standard entropy change for this reaction using the following data.
The standard free energy change, ΔGθ, for the above reaction is –103 kJ mol–1 at 298 K.
Suggest why ΔGθ has a large negative value considering the sign of ΔHθ in part (a).
Markscheme
ΔHθ = [–165.2 + 2(–296.9) + 2(–92.3)] – [–454.7 + 2(–245.7)]
«ΔHθ = +»2.5 «kJ»
Award [2] for correct final answer.
Award [1] for –2.5 «kJ».
Do not accept ECF for M2 if more than one error in M1.
«ΔSθ = [208.5 + 2(248.1) + 2(186.8)] – [166.9 + 2(278.6)]»
«ΔSθ = +» 354.2 «J K–1 mol–1»
«3 moles of» liquid to «4 moles of» gas
OR
«large» positive ΔS
OR
«large» increase in entropy
TΔS > ΔH «at the reaction temperature»
