naphta is a mixture (and not even a definite one), and as such does not have a chemical formula or standard free energy of formation.

https://en.wikipedia.org/wiki/Naphtha

Dear Sankalp,

you should have a look at some papers regarding the exergy of petroleum fractions:

Rivero et al.: The Exergy of Crude Oil Mixtures and Petroleum Fractions:

Calculation and Application, International Journal of Applied Thermodynamics, 1999

Furthermore, you should have a look at the book:

Szargut et al.: Exergy Analysis of Thermal, Chemical and Metallurgical Processes, Hemisphere Publishing, 1988

Providing information on how to calculate the exergy of fuels, if the elementary analysis is available or if the LHV or HHV are known.

As Gert Van der Zwan said, naphta is a complex mixture that have not a specific chemical formula, but the naphtha can be represented by a equivalent chemical formula based upon the atomic number of composition element (CHONS). And then, it can be calculated via the approach for calculating the chemcial exergy of organic fuel such as biomass, coal , and oil. I think this publication should help you.You may link to:

Modeling of chemical exergy of agricultural biomass using improved general regression neural network.