The tutor converts, for gasoline, the enthalpy of vaporization from Btu/gal to kJ/mol.

The density of gasoline is approx. 6.25lb/gal; its heat of vaporization is 900Btu/gal. Its molar mass is approx. 114g/mol. Then the conversion is

900Btu/gal x 1gal/6.25lb x 2.2lb/kg x 1kg/1000g x 114g/mol x 1055J/Btu = 38102J/mol = 38.1kJ/mol

Source:

walshcarlines.com

www.rapidtables.com

webbook.nist.gov

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.