Methanol Daily Question 091020007
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This post was last edited by Qingfeng Liushui on 2009-10-19 at 19:24. What is the activation energy of a catalyst? What impact does the level of activation energy have on production?
Generally, a catalyst can reduce the activation energy of a reaction, thereby accelerating its rate. However, a catalyst can not only speed up the forward reaction but also the reverse reaction; therefore, a catalyst cannot change the direction of the reaction! A good catalyst can reduce the activation energy significantly! Additionally, it should be said that activation energy mainly refers to the energy required for a chemical reaction to take place!
In general, reactant molecules must possess a high level of energy in order to be in an activated state and undergo a chemical reaction. This energy is generally much higher than the average energy of the molecules, and the difference between the two is the activation energy. At a certain temperature, the higher the activation energy, the slower the reaction; the lower the activation energy, the faster the reaction. For specific reactants and catalysts, the reactant molecules must cross the corresponding energy barrier in order to achieve chemical adsorption and thus undergo a chemical reaction. In short, the minimum energy required to convert ordinary molecules into activated molecules in a chemical reaction is the activation energy.
1\ Definition of activation energy (derived from kinetics) Activation energy refers to the minimum energy required, in a chemical reaction, for reactant molecules to become activated molecules. (The activation energy in the Arrhenius equation is different from the activation energy derived from kinetics; it is also known as the Arrhenius activation energy or empirical activation energy.) The activation energy is equal to the difference between the average energy of the activated molecules and the average energy of the reactant molecules. Taking enzymes and substrates as an example, the difference between the potential energy of these two in their free state and the potential energy of the activated molecule formed when they combine is the activation energy required for the reaction. Therefore, it is not that activation energy exists within cells; rather, certain forms of energy in cells provide the activation energy needed for the reaction. 2\ The rate of a chemical reaction is closely related to the value of its activation energy; the lower the activation energy, the faster the reaction rate. Therefore, reducing the activation energy effectively accelerates the progress of the reaction. Enzymes accelerate certain otherwise slow biochemical reactions by reducing the activation energy (actually by altering the reaction pathway to do so).
The minimum energy required to convert ordinary molecules into activated molecules in a chemical reaction is the activation energy. The higher the activation energy, the more difficult it is for molecules to become activated, thereby making chemical reactions more difficult to occur. The use of a positive catalyst alters the reaction pathway, reducing the activation energy required for the reaction and increasing its rate.