Numerical simulation is used to study an unstable, two-dimensional, two-stream, spatially developing, confined, reacting shear layer. The physical model is based on a low-heat-release, temperature-independent chemical reaction and is used to investigate the effect of the flow field on the burning rate at high Reynolds number and moderate Damkohler numbers. The unsteady mass, mometum, energy, and species conservation equations are integrated using a grid-free, Lagrangian field method in which gradients of the primary variables are transported along particle trajectories to preserve the numerical accuracy as strong strains arise in the flow. Results reveal a strong similarity between the distributions of product concentration and vorticity at a wide range of Damkohler numbers. This similarity is due to the entrainment field associated with vorticity amalgamation into large-vortex eddies. At low Damkohler numbers, products form in distributed zones within the large eddies, following the mixing of entrained reactants. At high Damkohler numbers, products form within thin zones around the outer edges of the eddies and then get entrained into the their cores. Between the large eddies, the strain field reduces product concentration by thinning the braids and reducing the time allowed for mixing. The effect of chemical kinetics rates on product formation is strongest around a Damkohler number of 1, and reaches its limit around Damkohler number of 20. Product formation is strongly governed by the entrainment field, and is thus weakly dependent on the Reynolds number. The reactants' ratio across the layer affects the rate of product formation, through the mechanism of asymmetric entrainment, by enforcing stronger potential of chemical activity.