ABSTRACT
Radioactive decay is a prominent example of a first-order reaction. At any given time, the velocity v of the decay reaction is proportional to the number N of radioactive molecules present, with the rate constant k as the proportionality constant: v=−dNdt=kNEq. To determine a rate constant for a chemical reaction, monitor the concentration(s) of reactant(s) or product(s) as a function of time, either continuously or discontinuously. The dependence of the concentration of the reactant as a function of time differs for first- and second-order reactions. To distinguish between first- and second-order reactions, plot the experimentally determined concentration of the reactant as a function of time, and try to describe the data with the integrated rate laws for first- and second-order reactions. Many enzymes need to associate to dimers to perform their biological functions. Examples are glutathione-S-transferase, alcohol dehydrogenase, transcription factors, and type II DNA restriction enzymes.
