Total heat?

Question

calculate the total heat (J) needed to convert 0.316 mol ethanol gas (C2H6O) at 151°C and 1 atm to liquid ethanol at 25.0°C and 1 atm.

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

molar mass of ethanol C2H6O = 2*12+6+16 =46
mass of ethanol 0.316*46 =14.536g
first step cool gas ethanol from 151C to 78.5
Q1 = m*cgas*(TF-TI)= 14.536*1.43(78.5-151)= -1507J
second step liquefaction of ethanol
Q2=-m*Hvap =-14.536*40.5 = -2096J
third step cool the liquid ethanol
Q3 = m*cliquid*(TF-TI)=14.536*2.45*(25-78.5) = -1905 J

and total heat Q= -1507-2096-1905=-5508 J

do not forget the sign - It is a cooling!