Physical chemistry
Potential energy surfaces and transition states
Potential energy surfaces map energy against nuclear coordinates; reaction paths cross a saddle point and transition state.
For many atoms, potential energy depends on many nuclear coordinates. A reaction is often pictured as a low-energy path connecting reactants and products.
Reaction paths and rates
Potential energy surfaces map energy against nuclear coordinates; reaction paths cross a saddle point and transition state.
Definition: Core definition
A transition state is the configuration at a first-order saddle point along a reaction path; it is not an isolable intermediate.
Example: Worked example
Apply the model to a simple case: In Eyring theory, raising ΔG‡ by several RT lowers the rate exponentially; temperature and activation entropy also affect the prefactor.
Solution
In Eyring theory, raising ΔG‡ by several RT lowers the rate exponentially; temperature and activation entropy also affect the prefactor.
A transition state is the configuration at a first-order saddle point along a reaction path; it is not an isolable intermediate.
| Quantity | Model / rule |
|---|---|
| Key relation | Potential energy surfaces map energy against nuclear coordinates; reaction paths cross a saddle point and transition state. |
| Meaning / use | In Eyring theory, raising ΔG‡ by several RT lowers the rate exponentially; temperature and activation entropy also affect the prefactor. |
What is the configuration at a first-order saddle on a reaction path called?
Which statement best matches the model described?
References
- H. Eyring, S. H. Lin and S. M. Lin (1980). The Theory of Rate Processes