Advances in microfluidics have inspired novel designs of LoC systems with integrated functionality and improved thermal and mass-transfer characteristics. As important functional subsystems of LoC, microfluidic reaction systems can significantly reduce the need for space, materials, and energy, and often have shorter response times. Iterative design studies require accurate and fast models for subsystems. Here, we present two PFR-network-based models and a method of lines model for reaction subsystems. These two models employ two different discretization methods to reduce the set of PDEs into a system of coupled ODEs. We use our model to analyze an example micro mixing-reaction system. The results illustrate how reaction channel length and the electric potential difference influence the product yields and selectivities. These models are ready to be combined other subsystem models for the design of integrated LoC systems.