A finite deformation formulation for reacting porous media with volume change

We develop a finite-deformation theory for reacting porous media consisting of a fluid andtwo solid phases (reactant and product). The central contribution is a kinematic and constitu-tive framework that distinguishes reaction-induced volume changes that merely fill pore spacefrom those that generate stress in the solid skeleton. This distinction is introduced througha distention-based decomposition of the deformation and a free-energy split into isochoric anddistention components. The theory also accounts for the evolving mechanical character of theskeleton by allowing its effective strength to update continuously as reactant is converted toproduct. In addition, we derive a generalized Darcy-like relative flux that consistently incorpo-rates fluid consumption by reaction and a thermodynamic driving force through the gradient ofthe exchange potential τ , a feature missing from standard reactive transport theories. The gov-erning equations are formulated in the reference configuration and cast in weak form for finiteelement implementation. Verification against analytical and standard poromechanics bench-marks demonstrates consistency of the formulation, and in the small-strain, non-reactive limitthe theory reduces to Biot poromechanics with B = 1.