Kinetics and Thermodynamics of Elementary Reversible Reactions in the Gas Phase

3-7 KINETICS AND THERMODYNAMICS OF ELEMENTARY REVERSIBLE REACTIONS IN THE GAS PHASE 

It is necessary to focus on details of the rate law iR before the mass balance. 

The principle of microscopic reversibility allows one to express the backward rate constant in terms of the forward rate constant divided by Kp, which is the equilibrium constant based on gas-phase partial pressures. Kp has units of pressure to the power 5, where 5 is the sum of the stoichiometric coefficients (i.e., 8 = —2 for this problem). Handbook values for standard-state free energies of formation at 298 K are used to calculate the Gibbs free-energy change for reaction at 298 K (i.e., 29s) thi to calculate a dimensionless 

One identifies the stoichiometric-coefficient-weighted sum of pure-component chemical potentials in the reference states, at unit fugacity, with the standard-state free-energy change for chemical reaction, since [pi, pure(/ )l° is equivalent to the molar Gibbs free energy of pure component i in this reference state. Hence, 

The equilibrium constant from thermodynamics is defined as follows in terms of fugacity ratios  

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