# Molecular Formula of different Octane rating gasolines?

#### Quds Akbar

Summary
Cannot find enthalpy of combustion of different gasoline mixtures because I cannot find their molecular formulas, since they are mixtures and not compounds, is there a workaround?
Trying to calculate the enthalpy of combustion for gasolines with different octane ratings, 95 and 91 gasoline in particular. The thing is, they are mixtures and not compounds. To calculate the enthalpy of combustion, I am trying to find the molecular formula for each of the gasolines, in order to work out the grams per mole. Is there a way to find the molecular formula for gasolines, or a workaround to finding the enthalpy of combustion for these different gasoline mixtures?

#### Borek

Mentor
If you know composition of the mixture, you can calculate its enthalpy of combustion as a weighted average.