Two or more equilibria can exist at the same time. When this is so, equilibrium constants can be ascribed to individual equilibria, but they are not always unique. For example, three equilibrium constants can be defined for a dibasic acid, HA.
:A + H  HA; 
:HA + H  HA; 
:A + 2 H  HA; 
The three constants are not independent of each other and it is easy to see that . The constants K and K are stepwise constants and β is an example of an overall constant.