When solutions of reactants $A$ and $B$ are stratified in a gravitational field and a second-order reaction $A+B\to C$ generates the product $C$ at the miscible interface, buoyancy-driven mixing between solutions can be affected by the reaction. To study this effect, we analyze how the reaction impacts density profiles. We compare theoretical predictions of convective scenarios based on these reaction-diffusion density profiles with nonlinear simulations of the incompressible Navier-Stokes equations coupled to reaction-diffusion-convection equations for the concentration of species $A, B$, and $C$. We analyze the dynamics in the parameter space $(R_B,R_C)$, where $R_B$ and $R_C$ represent the relative contributions of species $B$ and $C$ to the density of the bulk fluid compared to that of reactant $A$. We examine how varying $R_B$ and $R_C$ influence key flow characteristics, including the onset time of instability, the evolution of the reaction front, the mixing intensity, and the overall reaction yield. We find that the reaction can trigger convection in an initially statically stable stratification and intensify mixing in Rayleigh-Taylor unstable cases. Moreover, the reaction can influence the directionality of fingers and plumes depending on the relative contribution of the product to density compared to that of the reactants.

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• Fingering instability
• Flow instability
• Instability control
• Interfacial flows
• Pattern formation
• Rayleigh-Taylor instability
• Reacting flows
• Turbulent reacting flows