Reaction Mechanism

• A reaction mechanism provides detailed insight into how a chemical reaction progresses at the molecular level. It includes sequences of individual reaction steps that make up the overall chemical reaction.

• Reaction mechanisms can help us understand fundamentals like order of reaction and rate-determining steps in a chemical process.

• Not all steps in a reaction mechanism occur at the same speed. The slowest step is known as the “rate-determining step” because it determines the overall rate of the reaction.

• Partial reactions showing collision of two molecular species fall under the category of “elementary reactions”. Each of these reactions could be uni-molecular, bi-molecular or termolecular.

• Molecularity of a reaction refers to the number of molecules that participate as reactants in an elementary step. It’s important to note that the rate equation can only be derived directly from the reactants of the rate-determining step.

• Intermediates are species that are produced in one step and consumed in a subsequent step within the reaction mechanism. They do not appear in the overall equation for the reaction.

• Catalysts provide alternative reaction pathways with lowered activation energy, compared to the uncatalysed reaction. They act by providing a surface for the reactant particles to come together and react, increasing the likelihood of a successful collision.

• Reaction mechanisms must be consistent with the rate equation experimentally derived for the reaction. It is not a quirk of clever guesswork but must be supported by abundant experimental evidence.

• Reaction profile diagrams are used to represent energy changes during a reaction. They delineate the activation energy barriers for each step and help understand the reaction in detail along with the energy state of reactants, intermediates, transition states, and products.

• The Arrhenius equation connects the rate constant (k), temperature (T), activation energy (Ea), and the pre-exponential factor (A), and can be used to support evidence about reaction mechanisms.

Remember, understanding and being able to illustrate elements of the reaction mechanisms, such as rate-determining step, reaction intermediates and molecularity, are crucial for tackling questions about kinetics in Chemistry.