Question

From data below, calculate the total heat (in J) associated with the conversion of 0.229 mol ethanol gas (C2H6O) at 101°C and 1 atm to liquid ethanol at 25.0°C and 1 atm. (Pay attention to the sign of the heat.)

Boiling point at 1 atm 78.5°C

cgas 1.43 J/g°C

cliquid 2.45 J/g°C

H°vap 40.5 kJ/mol

Answer 1

To aswer this question, use molar mass to find grams of ethanol 0.505 moles ethanol @ 46.07gm/mol=23.265 grams of ethanol.

To cool the gas to 78.5⁰ C.

dH=23.265 g(1.43J/gm⁰C) (22.5⁰C)

dH = 748.55 Joules must be released

to condense the gas@ 78.5^oC

dH = nC

dH = 0.505 moles (40,500 Joules/mol)

dH = 20452.5 Joules

to cool the liquid to 25^oC

dH = m^oC dT

dH = 23.265 g ( 2.45 J/g⁰C) (53.5​⁰C)

dH = 3049.46 Joules released

that's a total of 24,250.5 Joules

at 3 sig figs

it rounds off to

dH total = - 24.3 kJ