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⋅Krespectively.

A. How much heat is required to convert 40.5

g of ethanol at 36 ∘C to the vapor phase at 78 ∘C?

B. How much heat is required to convert 40.5

g of ethanol at -161 ∘C to the vapor phase at 78 ∘C?

Answer 1

A)

mass of ethanol = 40.5 g

moles of ethanol = 40.5 / 46 = 0.88

specific heat of liquid ethanol = 2.3 J / g

Q = m Cp dT + n x deltaHvap

   = 40.5 x 2.3 x (78 - 36) x 10^-3 + 0.88 x 38.56

= 3.9123 + 33.95

= 37.86 kJ

heat required = 37.86 kJ

B)

- 161 oC ------ - 114 oC   ------------ 78 oC

Q1 = 40.5 x 0.97 x (- 114 + 161)

    = 1846.395 J

Q2 = 0.88 x 5.02 = 4.4176 kJ

Q3 = 40.5 x 2.3 x (78 - 114) = 3353.4 J

total heat required = 9.62 kJ