Stability constants
Stability constants
- The stability constant $K_{\text{stab}}$ measures how stable a complex is.
- It is the equilibrium constant for forming the complex in solution.
- It decides the direction of ligand exchange.
Practice
The stability constant K_stab is:
K_stab is the equilibrium constant for the complex-forming reaction; water is omitted.
What $K_{\text{stab}}$ tells you
- $K_{\text{stab}}$ is the equilibrium constant for forming a complex ion from the metal ion and its ligands (water is left out of the expression).
- A large $K_{\text{stab}}$ means a very stable complex.
Practice
A large K_stab means the complex is:
A large stability constant indicates a strongly favoured, stable complex.
Direction of ligand exchange
- In a ligand exchange, the equilibrium shifts towards the complex with the larger $K_{\text{stab}}$.
- So a ligand that forms a more stable complex can push out a weaker one.
Practice
In a ligand exchange, the equilibrium shifts towards the complex with the:
The more stable complex (larger K_stab) is favoured, so a stronger ligand can displace a weaker one.
You've got it
Key idea
- $K_{\text{stab}}$ = equilibrium constant for forming a complex (water omitted)
- a large $K_{\text{stab}}$ = a very stable complex
- ligand exchange moves towards the complex with the larger $K_{\text{stab}}$