Thermodynamics and kinetics Flashcards
What is gibbs of free energy equation?
change in G= change in H - T x Change in S
What is the gibbs free energy equation for equilibria
change in G= -RT lnK
How do ligand substitution reactions occur?
Stepwise. Each step can be given stepwise stability constant (K)
How do you work out stepwise stability constants?
Products over reactants
If there is no change in stereochemistry what happens to the value of K as you do further steps?
Decreases, due to statistics, less of the molecule to be substituted so less likely)
How do you get the formation constant (B)?
By multiplying all of the stepwise constants (K)
What is the chelate effect?
A complex formed with a chelating ligand is more thermodynamically stable than a complex formed with a monodentate ligand
What is a chelating ligand?
Polydentate ligand
What are the reasons for the chelating effect?
Entropic reasons- more free molecules released when a chelating ligand is used which increases the disorder.
Enthalpy- once one end of chelating ligand has bound not much organisation needed to bind the other end
What is the macrocyclic effect?
Even more increased stability than chelating effect. Ligand is already in correct shape to bind around the metal centre.
Driven by entropic factor- no need to lower entropy since already in correct shape
What is the main reason for the macrocyclic effect?
Entropic reason- already in the right shape to bind around the metal, it doesnt need to be organised
If you think about ligands in terms of lewis acids and bases, which would be which?
Lewis acid- metal (electron acceptor)
Lewis base- ligand (electron donor)
Even if thermodynamics of something are good reaction can still be slow, why?
Depends on the activation energy (amount of energy to get from initial to transition state)
What is a kinetically inert complex?
One which undergoes slow ligand substitutions (usually has high CFSE)
What is a kinetically labile complex?
One which undergoes fast reactions (usually has low CFSE)
