What is the principle of catalyst? Definition of catalyst: a substance that can significantly change the reaction rate and its chemical properties and quantity are basically unchanged before and after the reaction. Catalysts include positive catalysts (i.e. accelerating the reaction rate) and negative catalysts (i.e. reducing the reaction rate). Generally, they do not refer to positive catalysts. Catalytic principle: whether the chemical reaction can be carried out depends on the change of free energy, but it can not be judged whether the reaction can be completed only based on the change of free energy, because the completion of the chemical reaction also depends on the energy barrier of the reaction, that is, if the reaction energy barrier is very high, it must be provided with certain energy to cross the energy barrier to complete the reaction.

This energy barrier is called activation energy. The function of the catalyst is to reduce the activation energy and make it react in a relatively non harsh environment. The catalyst changes the reaction rate because it changes the reaction pathway and reduces the activation energy of the reaction. Principle of catalysis:

1. The phenomenon of accelerating or slowing down the rate of chemical reaction due to the intervention of catalyst is called catalysis. In the catalytic reaction, the catalyst and reactants have chemical interaction, which changes the reaction pathway and reduces the activation energy of the reaction, which is the reason why the catalyst can improve the reaction rate. For example, for chemical reaction a + B → AB, the required activation energy is e. after adding catalyst C, the reaction is carried out in two steps, and the required activation energies are f and g respectively, in which F and G are less than E.

2. A + C → AC ------ AC + B → AB + C, the activation energy of these two steps is much smaller than that of E. According to Arrhenius formula k = ae-e / RT, the E value decreases due to the participation of catalyst in the reaction, so the reaction rate is significantly increased. There are also some reactions. After the catalyst participates in the reaction, the activation energy E value changes little, but the pre exponential factor a value increases significantly (or interpreted as the increase of activation entropy), which also leads to the acceleration of the reaction rate.