Integrated SequencePhysics Chemistry Organic Biology

Web Resources

Purdue University - Catalysts and the Rates of Chemical Reactions
Good overview of the important principles of reaction catalysis.

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Special points of emphasis


Chemical Kinetics

Catalysts do not enter into the stoichiometric expression for a reaction because they are neither produced nor consumed in the reaction. As a consequence, the presence of a catalyst does not affect the underlying chemical thermodynamics of the reaction. The catalyst does not alter the internal energy change, enthalpy change, entropy change, free energy change or position of equilibrium.

This is such an important point that almost every MCAT will have you demonstrate in some question that you can separate chemical kinetics concepts, such as catalysis, from chemical thermodynamics questions, such as the position of equilibrium.

It is true that there is definitely a kinetics perspective on the equilibrium state. At equilibrium, after all, the forward and reverse reaction rates are equal. But a catalyst increases the rate of both the forward and reverse reactions. A catalyst does not alter the free energy change. A catalyst cannot alter the position of equilibrium.

Chemical Kinetics


Chemical kinetics concepts are crucial for the understanding of biochemistry. Most biochemical reactions are enzyme catalyzed, for example. There are many levels of complexity in enzyme catalysis involving mode, mechanism and feedback, which we will discuss in more depth when we reach the chapter on Proteins.

For now, just remember that the Michaelis-Menten equation expresses the relationship between the concentration of the reagent substrate and reaction rate. When the concentration is small, the rate is proportional to substrate concentration. When the concentration of substrate becomes so large as to saturate the enzyme, the rate is maximal, independent of substrate concentration. That is the big Michaelis-Menten concept that the MCAT expects you to be familiar with.

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