How to get Elemental Compositions

[sramjatan1]

Hello,

Sorry but I am forgetting how to calculate the elemental composition for the mixture file.
Is this the starting composition in mole fraction?

This is what I am trying to do:
I want to use the mppequil tool to get the equilibrium constant for a single reaction.
For example, lets say I am looking at CO + N => CN + O.

I then defined a mixture file with the species:
N, O, CN,O, and C.

I also defined a mechanism file with the rate parameters for the given reaction.

Now lets say I want the starting composition of all species to be 0.25 or the mass fractions to be
Y_CO=0.25,Y_N=0.25,Y_CN=0.25, and Y_O=0.25.

In my mixture file, I understand I need to specify the composition for C,O, and N.
But I am forgetting how to calculate what these values should be?

I hope my approach makes sense here?
I would appreciate any insight. Any links that will illustrate it better would be great.
Thanks for your time,

Sahadeo