A mathematical model was developed to interpret a liquid–liquid–solid heterogeneous reaction system using valeric acid (pentanoic acid) perhydrolysis as model. Kinetic, thermodynamic, and mass transfer parameters were included in this model. Perhydrolysis of valeric acid (pentanoic acid) on Amberlite IR-120 catalyst experiments were carried out in the temperature range of 40–60 °C and with an initial valeric acid concentration of 50 wt %. The influence of water and the acid catalyst was taken into account to develop a suitable kinetic model. The thermodynamic parameters, such as the reaction enthalpy (ΔHR0) and the molar equilibrium ratio (m) were determined experimentally. The kinetic parameters were determined by nonlinear regression analysis and they were statistically well-identified. The standard reaction enthalpy was estimated to −13.84 kJ·mol–1 and the activation energy of the reaction was estimated to 64.5 kJ·mol–1.