Question

Calculate the total heat (in J) associated with the conversion of 10.0 g of gaseous ethanol
(C2H5OH) at 78.5°C and 1 atm to liquid ethanol at 78.5°C and 1 atm.

Answer 1

T_boiling at 1 atm = 78.5⁰C

ΔH⁰_vap = 40.5 kJ/mol

Q = n*ΔH⁰_vap

n(C₂H₅OH) = 10.0 g/46.07 g/mol = 0.217 mol

Q = 0.217 mol * 40.5 kJ/mol = 8.791kJ = 8791 J

Q should be negative since the ethanol gives up energy

Q = -8791 J

Answer: -8791 J