There are two simple ways to do this,

• 1) Use expressions for the total chemical potential of each species and solve \sum \nu_i \mu_i. The summations will equal zero at the solution. Use a solver (excel works) to find the concentration that makes this sum equal 0. For instance you could assume your species are ideal gases. In this case you need for each species its reference chemical potential, this can be looked up in the back of most thermodynamic textbooks for this reaction.

mu_i = mu_i_ref + RT * ln x_i * P/Pref

mu_i is the total chemical potential

mu_i_ref is the reference chemical potential of species i, usually at temperature of 298.15 K and pressure of 1 bar

Pref is the reference pressure, usually 1 bar

R is the ideal gas constant

T is temperature

x_i is the mol fraction of species i

nu_i is the stoichiometric coefficient of species i in the reaction, reactants are given negative coefficients

• 2) Use equilibrium constants. These are not always known, but certainly are well documented for this reaction. This involves using an ICE table to solve for the extent of reaction.

Keq = activity of products / activity of reactants.

i.e. for A + 2B 3C + 4D

Keq = ( aC3 * aD4) / (aA * aB2)

usually you assume activity is equal to partial pressure if it is a gas phase reaction. If you use an equation of state you can calculate activity with no assumptions. There will be 1 unknown in this expression - the extent of reaction. Once you solve for it, you are done.

Here are some examples of using ICE tables. I cannot do formulas here so I won't try,

https://chem.libretexts.org/Textbook_Maps/Physical_and_Theoretical_Chemistry_Textbook_Maps/Book%3A_Physical_Chemistry_(Fleming)/9%3A_Chemical_Equilibria/9.4%3A_Degree_of_Dissociation

Thank you for such a nice answer i will try on this to solve.

Some example can be found here https://www.researchgate.net/deref/https%3A%2F%2Fchem.libretexts.org%2FTextbook_Maps%2FPhysical_and_Theoretical_Chemistry_Textbook_Maps%2FBook%253A_Physical_Chemistry_(Fleming)%2F9%253A_Chemical_Equilibria%2F9.4%253A_Degree_of_Dissociation