college chem
posted by john .
Ethanol (C2H5OH) boils at a temperature of 78.3oC.
What amount of energy, in joules, is necessary to heat to boiling and then completely vaporize a 20.0 g sample of ethanol initially at a temperature of 13.6oC.
The specific heat of ethanol is approximately constant at 2.44 JK1g1
The heat of vaporization of ethanol is 38.56 kJ mol1.

energy= mass*Lf+ mass*c*deltaTemp
look at the units of the constants.
Hv is in kJ per mole.
energy= moles*Lf+mass*c*deltaTEmp
now, for the first term, convert 20g ethanol to moles ethanol, and you have it. 
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