We study global decay of the bimolecular reaction A+B-->P as c(t)similar tot(-alpha) in a nonlinear transitional flow. A relationship is established between the decay exponent alpha, and a modified Kolmogorov-Sinai entropy, h(r). We find that for dynamic conditions which induce relatively strong mixing, the decay exponent is alphaproportional toln psi(r)(-Bh) with B being a characteristic reactive mix-down time for the system, and psi is a space-time scaling parameter. Dynamic conditions which imply weak mixing lead to a degenerate dependence of alpha on h(r). The proposed relationship between alpha on h(r) should be a useful link between the dynamical evolution of the flow field and reaction kinetics in vortex dominated flows. (C) 2004 American Institute of Physics.