Chemistry
posted by Cynthia .
The enthalpy of combustion of benzoic acid is –26.4 kJ/g. What is the enthalpy of
combustion expressed in joules per kilogram?

26.4 kJ/g x (1000 J/kJ) x (1000g/kg)

Could you explain how or why ?

I don't know that there is any explaining to do. To change kJ to J you multiply by 1000. There are 1000 g in a kg. Look at the dimensions. kJ in numerator cancel with kJ in the denominator to leave J/g after the first term. The second term cancels g and leave kg.