Concentration gradients provide a driving force for species movement, so they influence the direction and magnitude of transport fluxes. Chemical reactions can consume or generate species within the same region, reshaping those gradients over time. As a result, movement and transformation cannot always be analyzed independently when predicting concentration distributions or chemical performance.
Diffusion moves species in response to concentration differences, convection carries matter through bulk motion, and migration describes movement associated with another transport influence. Each mechanism contributes differently to species flux, while chemical reactions modify the concentrations that drive or accompany transport. Identifying the relevant mechanism is therefore essential for selecting an appropriate reaction transport model.
Rate laws describe how chemical transformations change species concentrations, whereas transport equations describe how those species move through a system. Coupling them shows how local reaction rates affect spatial concentration profiles and how transport supplies or removes reacting material. This combined description supports predictions that neither reaction kinetics nor transport analysis can provide alone.
Reactions can consume reactants or produce products, altering local concentrations and therefore changing concentration gradients and fluxes. These changes may vary from one location to another, especially in systems where matter travels through a reaction zone. Including reaction effects in the analysis helps explain why transport patterns and species distributions evolve as chemistry proceeds.
A model typically starts by identifying the chemical species and the relevant movement mechanisms. The analyst then combines mass balances with reaction rate laws and transport equations, applies the system conditions, and calculates concentration profiles or related outcomes. The resulting predictions can be used to evaluate reaction yields and assess how the system is expected to perform.
These processes are relevant in reaction vessels, porous materials, membranes, catalytic systems, and environmental media. In each setting, species may encounter different pathways for movement and chemical transformation. Modeling those coupled effects helps researchers and process designers examine concentration profiles, estimate reaction yields, and optimize the performance of chemical processes or materials.