A didactic sequence is proposed for the teaching of chemical equilibrium law. In this approach, we have avoided the kinetic derivation and the thermodynamic justification of the equilibrium constant. The equilibrium constant expression is established empirically by a trial-and-error approach. Additionally, students learn to use the criterion of comparison between equilibrium constant and reaction quotient to predict the direction of reaction. The teaching sequence takes into account the alternative conceptions and learning difficulties highlighted by teaching and research in science education and the need to focus on both the students' learning process and the knowledge on how to learn.