Physics and chemistry are closely related fields that interplay in many situations and processes, and share notions from quantum mechanics to thermodynamics. Chemistry can modify physical properties like density or temperature. Conversely, Physics plays a leading role for determining chemical constants. In this unit, we will study various situations including atmospheric or interstellar chemistry, but also theoretical systems resulting from the coupling between reaction, diffusion, and convection, to highlight, for instance, the emergence of propagating chemical reaction fronts.