Question

Ethanol, , boils at 78.29 °C. How much energy, in joules, is required to raise the temperature of 3.00 kg of ethanol from 38.0 °C to the boiling point and then to change the liquid to vapor at that temperature? (The specific heat capacity of liquid ethanol is 2.44 J/g ∙ K, and its enthalpy of vaporization is 855 J/g.)

Answer 1

Energy required = heat required to raise the temperature of ethanol to its boiling point + heat required to vaporize it.

Heat required to raise the temperature of a body by t:

H = mct, where m, c are mass and specific heats of the body respectively.

First, we calculate heat required to raise the temperature to boiling point :

m=3kg = 3000g, c =2.44 J/gK, t = 78.29 - 38 = 40.29 K

H = 3000 * 2.44*40.29 = 294922.8 J

Heat required to change state of a body = mL

Where m and L are mass and latent heat of fusion / melting respectively.

Here, m = 3000g and L = 855J/g

Hence, H= 3000 * 855 = 2565000J

Total energy = 294922.8 + 2565000 = 2859922.8 J