Rate of Reactions?

Question

Why do chemists tak the rate of reactions near the beginning of a reaction?

Answer 1

Well, as you know that the chemical reaction rate gets slower and slower due to the consumption of the reactant/s, unless the reaction is zero-order reaction, which is very unpopular. So at the very beginning, the chemists know the concentration of the reactants and thus associated reaction rate is meaningful for calculations. later on, the chemists either do not know the concentration of all the reactants, or the reaction rate is zero at the very end of the reaction, so he data would be less meaningful.