Question

Enter your answer in the provided box. From the data below, calculate the total heat (in J) needed to convert 0.579 mol of gaseous ethanol at 300.0°C and 1 atm to liquid ethanol at 25.0°C and 1 atm: b.p. at 1 atm: 78.5°C ΔH o vap : 40.5 kJ/mol cgas: 1.43 J/g·°C cliquid: 2.45 J/g·°C

Answer 1

Before calculating the haet change you need to conver 0.579 mol to g as the specific heats are in j/g c

0.579 mols of C2H5OH = 0.579 * 46 = 26.63 g

calculate the heat change in 3 stages

1) the heat required to cool down the gas from 300 c to 78.5 c ( this will be negative - heat out)

heat change = mass * C * change in temperature = 26.63 g * 1.43 j/g c * -221.5 c = -8435 J

2) the heat change required to condense the gas to liquid at 78.5 c

= moles * heat of vapourizaion

= 0.579 moles * -40.5 KJ / mol = -23.449 KJ = ( - 23,449 J)

3) the heat required to cool down the liquid from 78.5 c to 25.0 c

= mass * C * change in temperature = 26.63 g * 2.45 J / g c * -53.5 c = -3490 J

total heat rwquired = -8435 J - 23,449 J - 3490 J = -35,374 J