The enthalpy of combustion of hard coal averages - 35 kJ/g, that of gasoline, 1.28 x 105 kJ/gal. How many kilograms of hard coal provide the same amount of hat as is available from 1.0 gallon gasoline? Assume that the density of gasoline is 0.692 g/mL (the same s density of isooctane).

3.657 kg

Explanation:

Given:

Enthalpy of combustion of hard coal = - 35 kJ/g

Enthalpy of combustion of gasoline = 1.28 * 10⁵ kJ/gal

Density of gasoline = 0.692 g/mL

now,

The heat provide 1 gallon of gasoline provide = 1.28 * 10⁵ kJ

and,

heat provided by the 1 gram of coal = 35 kJ

or

1 kJ of heat is provided by (1/35) gram of hard coal

therefore,

For 1.28 * 10⁵ kJ of heat, mass of hard coal = 1.28 * 10⁵ kJ * (1 / 35)

or

For 1.28 * 10⁵ kJ of heat, mass of hard coal = 3657.14 grams = 3.657 kg