So far in our discussion of chemical reactions we have assumed that these reactions only go in one direction, the forward direction, from left to right as we read it in an equation. That's why our arrow points from left to right: reactants react together to make products. However, this is not exactly how things occur in nature. In fact, practically every chemical reaction is reversible, meaning the products can also react together to reform the reactants that they were made of. So instead of writing that single arrow facing from left to right, a more appropriate symbol would be a double arrow, one going from left to right and one going from right to left. Reactants are continually - continuously - reacting to form products. But at the same time as those products are formed, they remake the reactants. They're both going simultaneously, forming each other. This is what we would call a state of equilibrium.