Question

Ethanol (C2H5OH) melts at -114 ∘C and boils at 78 ∘C. The enthalpy of fusion of ethanol is 5.02 kJ/mol, and its enthalpy of vaporization is 38.56 kJ/mol. The specific heat of solid and liquid ethanol are 0.97 J/g⋅K are 2.3 J/g⋅K respectively. Q: A) How much heat is required to convert 36.5 g of ethanol at 35 ∘C to the vapor phase at 78 ∘C? B) How much heat is required to convert 36.5 g of ethanol at -167 ∘C to the vapor phase at 78 ∘C?

Answer 1

A)

mass of ethanol = 36.5 g

moles of ethanol = 36.5 / 46.07 = 0.7923

35 -------- 78 oC

Q = m Cp dT + n x deltaHvap

    = 36.5 x 2.3 x (78 - 35) + 0.792 x 38.56 x 10^3

    = 3609.85 + 30551

Q = 34161 J

heat required = 34.16 kJ

B)

- 167 -------- - 114 ---------- 78

Q1 = 36.5 x 0.97 x (167 - 114)

      = 1876.46 J

Q2 = 0.7923 x 5.02 x 10^3

       = 3976.84 J

Q3 = 36.5 x 2.3 x (78 + 114)

     = 16118.4 J

Q4 = 0.7923 x 38.56 x 10^3

      = 30551 J

total heat = Q1 + Q2 + Q3 + Q4

                 = 52522.8 J

heat required = 52.52 kJ