Chemical equilibrium is a status quo condition that comes about when the opposing actions are offsetting.

If you are unfamiliar with the concept of chemical equilibrium, visit An Introduction to Equilibrium [Local] and learn about the equilibrium condition. [Local].

A chemical equilibrium is a dynamic [Local] situation, one that is changing all the time, but whose changes are offsetting.

Conditions that influence equilibrium include temperature, pressure, and concentration. Changing these conditions can cause the equilibrium to shift from an initial status or position to a new status or position.

The requirements for a chemical equilibrium to be able to exist are that the reaction must be reversible and the system must be closed (to prevent loss of any reactant or product).

An equilibrium condition may be established rapidly; on the other hand, it may take a very long time for equilibrium to be reached. Once a system has reached equilibrium the properties of the system that we can measure (e.g. temperature, pressure, concentration) will become constant. All reacting species represented in a chemical equation will be present in a system that has reached chemical equilibrium.

Equilibrium conditions can exist for both physical changes and chemical changes. Because they are conceptually a bit simpler, equilibria of physical changes will be examined first.