Re: Why are rate constants important when we can find out speed experimentally

It is possible indeed to determine the rate of a reaction at constant temperature experimentally. The real advantage of determining the rate constant is described below, using a broad example.

For instance, in industry, suppose one is interested in synthesizing a molecule using a reaction. To ensure that the reaction is run most efficiently (bottom line = cheaply) a number of variables have to be studied -- temperature, concentration of reactants, catalyst choice, solvent choice, etc. Also, these reactions have to be run at various scales -- starting from a few mg to multiple kgs.

It is impossible to calculate the rate including all these possible variations experimentally since this would run to hundreds of experiments. Instead, if we can run the reaction and measure the experimental rate at a few temperatures then it is possible, using the rate constant, to determine the rate at any other given T and concentration of reactants - so it is possible to have a big-picture view of the reaction and then choose appropriate conditions that will give the most yield and productivity.

In reality this is done routinely in industry. Also, determining the rate constants forces one to establish the mechanism of the reaction (is it series, parallel, consecutive, first order, second order, etc.), such that with this knowledge one may be able to understand the effects of the type of catalyst, impurity levels, etc.