The acid and base equilibrium constant expressions describe the relationship between the amounts of reactants and products in aqueous acid-base systems. For the following general weak-acid equilibrium:
![image0.jpg](https://www.dummies.com/wp-content/uploads/323992.image0.jpg)
the equilibrium constant expression is:
![image1.jpg](https://www.dummies.com/wp-content/uploads/323993.image1.jpg)
For a general weak-base equilibrium:
![image2.jpg](https://www.dummies.com/wp-content/uploads/323994.image2.jpg)
the equilibrium constant expression is:
![image3.jpg](https://www.dummies.com/wp-content/uploads/323995.image3.jpg)
The concentration of water (or any pure liquid or solvent or solid) does appear in the equilibrium constant expression. K is the equilibrium constant, the subscript b indicates that this is an equilibrium constant expression for a weak base, and the brackets indicate molar concentrations.