For gas liquid reaction systems with inlet and outlet streams, this paper proposes a linear transformation of the numbers of moles into five distinct parts, namely, the extents of reaction, the extents of mass transfer, the extents of inlet flow, the extents of outlet flow, and invariants. Furthermore, we discuss several implications of being able to compute the various extents directly from the measured numbers of moles without knowledge of kinetic and mass-transfer rate expressions. The computation of extents is illustrated via the simulation of different reactor configurations for the chlorination of butanoic acid.