Using linear combinations of vectors in composition space, we formulate a lever rule for reactive distillation columns. This lever rule facilitates the proposal of alternative sequences of reactive distillation systems by allowing us to visualize how material balance constraints move as a Function of reaction "turnover". our approach uses the concept of a pseudo-feed, which is the composition that results from mixing column distillate and bottom products. Our lever rule for reactive distillation columns uses linear combinations of so-called reaction difference points, stoichiometric coefficient vectors of reactants and products, and composition vectors. When a reaction causes no change in the total number of moles, the reaction difference point moves to infinity (Hauan, Omtveit & Lien (1996). Paper 5f, A.I.Ch.E. Annual Meeting, Chicago, Hauan, Westerberg & Lien (1999a). Chemical Engineering Science, 55(6), 1053-1075, Hauan, Ciric, Westerberg & Lien (1999b). Chemical Engineering Science, in press). We show how to carry out all geometric constructions entirely within a finite composition domain by decomposing the total stoichiometric coefficient vector into product and reactant stoichiometric coefficient vectors. In this case the lever rule compares distances along two parallel vectors. For an infinite extractive difference point (Westerberg & Wahnschafft (1996). Advances in Chemical Engineering, 23, 63-170) we can confine all geometric manipulations when proposing alternative reactive distillation processes to a finite composition domain by combining the vectors in a different order.