Combining Equilibrium Constants
The rule that when two reactions are added, their equilibrium constants multiply.
Formula / equation
K_overall = K₁ × K₂
Unit
Various
In depth
The rule follows from the mass action expressions, where the common intermediate cancels between numerator and denominator. It is the equilibrium counterpart of Hess's law and lets constants for reactions that cannot be measured directly be assembled from those that can.
Examples in the real world
Multiplying the two stepwise ionisation constants of carbonic acid gives the overall constant for losing both protons.