What is the Difference Between Stepwise and Overall Stability Constants?

The difference between stepwise and overall stability constants lies in their application and derivation in the process of ligand substitution:

• Stepwise Stability Constants: These are equilibrium constants given for each step of the process of ligand substitution. When a transition metal ion complex has water ligands surrounding the metal ion, the ligand substitution takes place as a stepwise process, where only one water molecule is replaced by the ligand involved in the substitution. The values of stepwise stability constants are lower than the overall stability constant.
• Overall Stability Constant: This is the equilibrium constant of the overall reaction. The overall stability constant is given for the whole substitution reaction that takes place in a coordinate complex. The overall stability constant is always higher in value than each stepwise stability constant.

In summary, stepwise stability constants are relevant to individual steps in a ligand substitution process, while the overall stability constant represents the entire substitution reaction. The overall stability constant is typically higher in value than the stepwise stability constants.

Comparative Table: Stepwise vs Overall Stability Constants

The difference between stepwise and overall stability constants can be summarized in the following table:

In summary, stepwise stability constants are equilibrium constants for each step of the ligand substitution process, while the overall stability constant is the equilibrium constant for the entire substitution reaction. The values of stepwise stability constants are lower than the overall stability constant.