Chemical equilibrium is a state in which the rate of the forward reaction equals the rate of the backward reaction. In other words, there is no net change in concentrations of reactants and products. This kind of equilibrium is also called dynamic equilibrium and can be used in a wide range of processes including both chemical and physical changes. An equilibrium is a situation whereby the quantity or quality of the sample does not change in time. Such a situation is intimately connected to "thermodynamics" as discussed in previously. As you will learn in Chem 2CH, electrochemistry is the third member of this troika.