# Specific Heat Ratio - Rocketry

by mrjeffy321
Tags: heat, ratio, rocketry, specific
 Sci Advisor PF Gold P: 1,479 If I were you I'd do: $$\gamma_{average}=\frac{\sum X_i C_{pi}}{\sum X_i C{vi}}$$ where Xi is the molar fraction of the i-th chemical product.
 Sci Advisor PF Gold P: 1,479 Specific Heat Ratio - Rocketry Sorry, I forgot to say that Cp_i and Cv_i are the molar heat capacities. I think you will obtain the same number (or at least a very close number to that) if you calculate it by means of the mass fraction and the mass heat capacities. The fact is such coefficients are calculated assuming an equal energetic state of both the complete mixture and the sum of the components: $$U=N_{total}C_{Vaverage}T)_{average of the mixture}=\sum U_i$$ If you start from that point, using a mass weighted average or molar weighted average you will obtain an equivalent number for Cv (molar or mass based).