What is the principle of catalyst? The definition of catalyst is a substance that can significantly change the reaction rate while its chemical properties and quantity remain essentially unchanged before and after the reaction. Catalysts include positive catalysts (which accelerate the reaction rate) and negative catalysts (which reduce the reaction rate), and are generally referred to as catalysts unless otherwise specified. The catalytic principle states that whether a chemical reaction can proceed depends on the change in free energy. However, relying solely on the change in free energy cannot determine whether the reaction can be completed, as the completion of a chemical reaction also depends on the energy barrier of the reaction. That is, if the energy barrier of the reaction is high, a certain amount of energy must be provided to cross it and complete the reaction.
This energy barrier is called activation energy. The role of the catalyst is to reduce the activation energy, allowing it to undergo chemical reactions in relatively less harsh environments. Catalysts change the reaction rate by altering the reaction pathway and reducing the activation energy of the reaction. The principle of catalytic action:
1. The phenomenon of accelerating or slowing down the rate of chemical reactions due to the intervention of catalysts is called catalytic action. In catalytic reactions, the catalyst undergoes chemical reactions with reactants, changing the reaction pathway and thereby reducing the activation energy of the reaction, which is the reason why the catalyst can increase the reaction rate. For the chemical reaction A+B → AB, the required activation energy is E. After adding catalyst C, the reaction proceeds in two steps, and the required activation energies are F and G, respectively, where F and G are both less than E.
2. A+C → AC -------- AC+B → AB+C, the activation energies of these two steps are much smaller than the E value. According to the Arrhenius formula k=Ae-E/RT, the participation of the catalyst in the reaction reduces the E value, thereby significantly increasing the reaction rate. There are also some reactions where the activation energy E value does not change significantly after the catalyst participates in the reaction, but the pre exponential factor A value increases significantly (or is explained as an increase in activation entropy), which also leads to an increase in reaction rate.
