I'm not sure if
the hydrocarbons are your actual goal or just an example, but if you're
really interested in their density and would like to correct them for the same
reference temperature, maybe you could start with standard methods devoted to
this issue. For instance, back in the day when I worked for some oil companies,
we used ASTM D1298 standard method (along with standard tables and equations
specified by the method) to measure the densities of petroleum products, which
had to be corrected to 15 °C. In short, we had a different correction
factor per unit °C which was different for different kinds of petroleum
products (saturated, unsaturated or aromatic).
engineering-related approach, a more science-based approach would take the
thermal expansion for each individual substance (ASTM methods use average
corrections for a whole class of substances) and would correct the individual
densities to a reference temperature.