Let's say I have a heat capacity ratio of 1.4 N2 and a heat capacity ratio of 1.2 for O2 (just random placeholder values no significance), and I wanted to calculate the heat capacity ratio of their mixture, similar to air let's say 80% N2, 20% O2 (again placeholder values).
How would I go about calculating the heat capacity ratio of air in total? I have seen people say that I should find the molar fractions of N2 and O2, and then multiply the fractions by the heat capacity ratio.
BUT, I have also seen a solution manual from Thermodynamics: An Engineering Approach, instead use the mass fractions of N2 and O2, and then multiply the fractions by the specific heat capacity at a constant pressure. Then once you find the specific heat capacity at a constant pressure of the mixture, you then use Cv=Cp - R, to find the specific heat capacity at a constant volume, and then do Cp/Cv to get the heat capacity ratio of the mixture.
Can anyone confirm the correct method? And unfortunately I have checked, you do not get the same answer.