Molecular mass of He+MON and He+MMH

[hamzaaaa]

Dear all

I have a case. I have two tanks, one is filled with Helium gas and monomethylhydrazine(MMH) and another tank with Helium gas and Dinitrogentetraoxide(MON). Both tanks are at 47degC so they are in gaseous form.

I want to know what will be the Molecular Mass of the gas. The molecular mass of He=4 g/mol,MMH=46 g/mol and MON=92 g/mol.

So can anyone tell me what will be the molecular mass i should use for computations for (He+MMH, He+MON and He+MMH+MON)

Thanks

 

[Borek]

For some applications you can use weighted average - but calculation requires knowing composition of the mixtures.

 

[hamzaaaa]

But why to take the average and why not the sum of all three?

 

[Borek]

Because some properties scale as the average of the molar mass.

Solve this problem: you mix 0.5 L He and 0.5 L Ar. What is the density of the mixture?