The Chemical Equilibrium Constant represented by `K_a` can be expressed therefore in terms of system Pressure and the mole fraction of component i in the gas. For reaction `aA + bB harr cC +dD`, for mixtures of ideal gases, the partial pressure of component i is equal to the fugacity of component i. The relationship is expressed in 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