Question

Calculate the total energy (in joules) needed to convert 15.0 grams of liquid ethanol at 25 0C to gas at 78 0C (boiling point). The specific heat of ethanol is 2.46 J/g 0C and the heat of vaporization is 841 J/g.

Answer 1

Energy needed to raise the temperature from 25 ^oC to 78 ^oC = m x s x

where,

m = mass of ethanol = 15.0 g

s = specific heat of ethanol = 2.46 J/g ^oC

= temperature difference = (78 - 25) ^oC = 53 ^oC

Hence,

the energy needed to raise the temperature from 25 ^oC to 78 ^oC = 15.0 g x 2.46 J/g ^oC x 53 ^oC

                                                                                                       = 1956 J

Energy needed to evaporate ethanol = m x

where,

= 841 J/g

Thus,

the energy needed to evaporate ethanol = 15.0 g x 841 J/g = 12615 J

Hence, the total energy needed = 1956 J + 12615 J

                                                   = 14571 J

                                                   = 1.46 x 10⁴ J