How do catalysts alter the mechanism of a reaction?

Catalysts alter the mechanism of a reaction by providing an alternative reaction pathway with a lower activation energy.

Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. They achieve this by providing an alternative reaction pathway that has a lower activation energy than the original pathway. The activation energy is the minimum amount of energy required for a reaction to occur. By lowering this energy barrier, more reactant particles have sufficient energy to react, leading to an increase in the rate of reaction.

The way catalysts work is by forming temporary bonds with the reactant molecules, creating an intermediate species. This intermediate species is more reactive than the original reactants, allowing the reaction to proceed more easily. The catalyst is then released unchanged at the end of the reaction, ready to participate in the process again. This is why catalysts are not consumed in the reaction.

Catalysts can be either homogeneous or heterogeneous. Homogeneous catalysts are in the same phase as the reactants, while heterogeneous catalysts are in a different phase. Homogeneous catalysts typically work by forming a temporary complex with the reactants, which rearranges to form the products and release the catalyst. Heterogeneous catalysts, on the other hand, often work by adsorbing the reactants onto their surface, where the reaction occurs more easily.

In addition to increasing the rate of reaction, catalysts can also influence the mechanism of the reaction. The mechanism of a reaction is the step-by-step sequence of elementary reactions by which overall chemical change occurs. A catalyst can change the mechanism by providing a different sequence of steps that has a lower overall activation energy. This can also lead to different products being formed, if the catalyst provides a pathway for a different reaction to occur.

In summary, catalysts alter the mechanism of a reaction by providing an alternative reaction pathway with a lower activation energy. They do this by forming temporary bonds with the reactants, creating an intermediate species that is more reactive. This allows the reaction to proceed more easily and quickly, and can also lead to different products being formed.