To study chemical equilibrium of hadronic matter created in relativistic heavy ion collisions, phase shifts for the I = 2ππ elastic scattering and cross sections for the I = 2and0ππ ( →) ρρ and I = 0ππ(→)ωω reactions are calculated with the prior and post forms. While the post-prior equivalence holds for the elastic scattering,the post-prior discrepancy of the inelastic scatterings relies on the spin-dependent terms of quark-antiquark potential.