A program of analysis is carried out for observation and control of a stirred tank reactor within an Input-Output linearization framework. The observer is employed to generate conversion estimates for the CSTR under output feedback control using only temperature measurements; specifically, nth-order non-isothermal reactions are considered. Analysis of the resulting closed-loop system rigorously confirms the separation principle. Thus, even though the observer estimates are not arbitrarily fast, convergence of the closed-loop system is always achieved.