A 0.50 mol sample of liquid ethanol at 25 °C is converted to superheated ethanol…
CHEMISTRY · Single correct · A Level · Chemistry · Thermodynamics · Thermodynamics
Problem
A 0.50 mol sample of liquid ethanol at 25 °C is converted to superheated ethanol vapor at 95 °C and 1 atm by two different routes.
Route I: (a) Reduce the external pressure so the ethanol vaporizes at 25 °C; (b) heat the vapor from 25 °C to 95 °C at 1 atm.
Route II: (a) Heat the liquid from 25 °C to 78 °C at 1 atm; (b) vaporize the ethanol at 78 °C and 1 atm; (c) heat the vapor from 78 °C to 95 °C at 1 atm.
Which statement is true concerning the entropy change of the ethanol, ΔS₍ethanol₎, for the two routes?
(a) ΔSethanol is larger for Route I because vaporisation occurs at a lower temperature, and ΔS=Tqrev is greater when T is lower.
(b) ΔSethanol cannot be determined without knowing ΔHvap at both 25∘C and 78∘C.
(c) ΔSethanol is identical for both routes because entropy depends only on the initial and final states.
(d) ΔSethanol is larger for Route II because warming the liquid before it vaporises supplies additional heat that increases entropy.