`K_a` (pressure, Ideal gas)

The Chemical Equilibrium Constant represented by `K_a` can be expressed therefore in terms of pressures.   For reaction the general chemical reaction `aA + bB harr cC + dD`, which are mixtures of ideal gases the partial pressure of component i is equal to the fugacity. This relationship is built upon the definition of partial pressure of the component i such that:

       `hatf_i` = `y_iP` = `p_i`    where:

             `hatf_i` = fugacity of component i  ,

             `y_i` = mole fraction of component i in the gas, and

             `P` = system Pressure