Question

How much heat energy is required to convert 81.5 g of solid ethanol at -114.5 °C to gasesous ethanol at 194.1 °C? The molar heat of fusion of ethanol is 4.60 kJ/mol and its molar heat of vaporization is 38.56 kJ/mol. Ethanol has a normal melting point of -114.5 °C and a normal boiling point of 78.4 °C. The specific heat capacity of liquid ethanol is 2.45 J/g·°C and that of gaseous ethanol is 1.43 J/g·°C.

Answer 1

moles of ethanol = 81.5/46 = 1.77 moles.

a. heat to convert solid to liquid at -114.5 degrees celcius

q = deltaHfusion* moles

    = 4.6*1.77 = 8.142 KJ

b. heat liquid ethanol from -114.5 degrees celcius to 78.4 degrees celcius

q = msdeltaT

   = 81.5*2.45*(78.4-(-114.5))

   = 38517 J

c. heat to convert liquid to vapor

q = deltaHvaporization*moles

   = 38.56 *1.77

   = 68.25 KJ

d. heat steam from 78.4 degrees celcius to 194.1 degrees celcius

q = msdeltaT

   = 81.5*1.43*(194.1-78.4)

   =13484.3 J

Total energy = 8.142 KJ + 38.517 KJ + 68.25 KJ + 13.484 KJ

                     = 128.393 KJ