Reversible reaction

A reversible reaction may not go to completion. As products form, some can react to re-form the reactants, so the final mixture still contains reactants.

In many equations, a single arrow shows reactants changing into products. However, in a reversible reaction, the products can themselves react and form the original reactants again. The reaction can therefore proceed in two directions.

In a reversible reaction, those products can also react to make the original reactants. We call the first direction the forward reaction and the returning direction the reverse reaction.

Unreacted material or a reversible reaction points to less product being formed; product left in a solution or on equipment points to incomplete recovery. When judging a given procedure, identify which explanation its details support rather than listing every possible cause.