Equilibrium is a state of balance between opposing forces such that the net force or change is zero, including static equilibrium where the resultant force is zero and dynamic equilibrium where the rates of opposing reactions are equal. There are different types of equilibrium such as chemical, dynamic, and ionic equilibrium. A contact equilibrium separation process aims to reduce the concentration of a component in one phase or stream and increase it in another, typically calling one stream the overflow and the other the underflow.