Magnitudes and Units of Rate Constants

If chemists want to compare reactions to evaluate which ones are relatively fast and which ones are relatively slow, the quantity of interest is the rate constant. A good general rule is that a large value of k ( 10 or higher) means a fast reaction and a small value of /c (10 or lower) means a slow reaction. 

The units of the rate constant depend on the overall reaction order of the rate law. In a reaction that is second order overall, for example, the units of the rate constant must satisfy the equation  

Units of rate = (units of rate constant) (units of concentration)  

in our usual units of molarity for concentration and seconds for time, we have 

Determining Reaction Orders and Units for Rate Constants 

Suppose the reactions A--- B and X---- Y have the same value of k. When 

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