Let's take water for an example: the specific heat for water vapor is 1.99. This would mean that the molar specific heat is the molar mass times the specific heat (or $18.0*1.99 = 35.8$).
- Is 35.8 J/mol*K at constant volume, $C_v$, or constant pressure, $C_p$?
- Why can't you calculate the molar heat capacity directly for water vapor using $3R = 24.94 J/mol*K$ for constant volume and $4R = 33.26 J/mol*K$ for constant pressure? Why don't these values match up with the 35.8?