Siirtymätilateoria

Siirtymätilateoria, often translated as Transition State Theory (TST), is a fundamental concept in chemical kinetics that describes the rates of chemical reactions. It proposes that for a reaction to occur, reactants must pass through a high-energy, unstable intermediate state known as the transition state. This transition state represents the peak of the energy barrier that must be overcome for the reaction to proceed to products.

The theory posits that the rate of a reaction is directly proportional to the concentration of this transition state and the frequency at which it decomposes into products. Central to TST is the assumption that the transition state is in quasi-equilibrium with the reactants. This allows for the calculation of the rate constant using thermodynamic quantities, particularly the free energy of activation.

Key parameters in TST include the activation energy, which is the energy difference between the reactants and the transition state, and the pre-exponential factor, which relates to the frequency of molecular collisions and the probability of them occurring with sufficient energy and proper orientation. While TST provides a powerful framework for understanding reaction rates, it relies on several approximations, such as the assumption of separable vibrational modes and the neglect of recrossing events. Despite these simplifications, Transition State Theory remains a widely used and valuable tool in chemical research and education.