Abstract: A modelling system models a physicochemical process such as a chemical reaction process (1) with mass and heat transfers across liquid, gas, and solid phase boundaries. A model editor receives a components file (2(a)) of chemical species, a natural language process description, (2(b)), a scenarios file (2(c)) having multiple rows (records) each for a different set of conditions, and an experimental data file (2(d)). A validation function (24) parses the input files and also simultaneously automatically builds equations using rules associated with the process description. A simulator function executes a validated model comprising the built equations and data and integrates the equations by determining source and sink values at time steps.