What do catalysts do in chemical reactions?

Catalysts play a crucial role in chemical reactions by lowering the activation energy required for the reaction to proceed. This reduction in activation energy allows the reaction to occur more readily and often at a faster rate, without the catalyst being consumed in the process. By facilitating the formation of the transition state, catalysts make it easier for reactants to convert into products.

In essence, catalysts serve to provide an alternate pathway for a reaction, which requires less energy compared to the uncatalyzed reaction. They are typically not involved in the overall stoichiometry of the reaction, meaning they are not diminished or changed in quantity during the reaction, allowing them to be used repeatedly.

In contrast, increasing the pressure can influence gas-phase reactions but does not directly pertain to the function of catalysts. Color changes of the reaction mixture may occur during chemical reactions, but this is not a defining characteristic or purpose of catalysts. Additionally, catalysts are not consumed in reactions, so any option that suggests they are consumed contradicts their fundamental nature. Thus, the correct understanding is that catalysts primarily work by lowering the activation energy of chemical reactions.