In this work we study the stabilization of continuous stirred tank reactors with unknown reaction rates. We prove that, under certain general assumptions, the chemical reactor can be stabilized with high-gain feedback. Simulations show that high-gain feedback may lead to hard input saturation and poor closed-loop performance. A reaction rate uncertainty estimator is introduced which, when coupled with a nonlinear feedback, leads to global stability with acceptable control performance. We conclude that state observation is unnecessary for the stabilization of the class of chemical reactor considered here.