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A Brief Look at Catalysts

We all have heard of catalysts. In lay terms we know that catalysts speed up reactions. But the question is how do they accomplish this? Consider the formal definition of a catalyst.


A catalyst is a chemical substance that can increase the rate of a reaction. Even if the catalyst is involved in the reaction, by the end of the reaction you will get the catalyst intact. In other words, the catalyst retains its identity. If a substance changes its identity and does not have the original nature after the reaction has occurred, it is not a catalyst, but a reactant.


As we said earlier, the activation energy is the minimum energy required by the reactants to reach the transition state. A catalyst lowers the activation energy of a reaction. Thus it provides a lower energy pathway for the reaction to occur. So the transition state bump in the potential energy diagram (see Figure 11-2) is lowered in a catalyzed reaction, compared to the corresponding uncatalyzed reaction.

image\15095 ch 11.png


Catalysts are often classified on the basis of the phases (solid, liquid, and gas) in which they exist during a chemical reaction. If a catalyst exists in the same phase as the reactants of a reaction, then it is called a homogeneous catalyst. If a catalyst's phase is different from that of the reactants of a reaction, then it is called a heterogeneous catalyst.

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