I have a mixture with 1 part of gas A, and 7 parts gas B. This ratio is in terms of mass.

Gas   Molar Mass (kg/mol)
A     0.17034
B     0.034

I'm trying to find the specific gas constant of the mixture.

$$ R_{\text{sp}} = \frac{R}{M} $$

I thought it might be $$ M = 0.17034\frac{1}{8} + 0.034\frac{7}{8} $$ but I can't work out if that makes sense given the units, or whether I should be using atomic mass or something.


1 Answer 1


The molar mass $(M)$ of a mixture with known mass fractions $(w_{i})$ is calculated from:

$$ \frac{1}{M} = \sum_{i}\frac{w_{i}}{M_{i}} $$

So in this case $$ \frac{1}{M} = \frac{1/8}{0.17034}+\frac{7/8}{0.034} = 26.469\ldots\\ M = \frac{1}{26.469\ldots} = 0.037779872\ \mathrm{kg}/\mathrm{mol} $$


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.