Question

What is the importance of knowing the reaction rates? What is the meaning of a positive sign in the average rate of the reaction? What is the meaning of negative sign in the average rate of the reaction?

Answer 1

To answer this question, you must recall the formula for rate of reaction. Along with the feasibility and extent of a reaction, it is equally important to know the rate of a reaction for its complete understanding. It is expressed as a change in concentration of reactants or products w.r.t. time.

Complete answer:
While studying a chemical reaction, it is important for us to consider not only the chemical properties of the reactants, but also the conditions under which the reaction is taking place, the mechanism by which it is proceeding, the rate at which it is occurring, and the equilibrium toward which it is moving.
It is important to know the rate of a reaction because knowing it can help us adjust the reaction conditions in order to obtain a more suitable rate and a more effective and efficient reaction. If we have two competing reactions for a given set of reactants, the knowledge of the rate can help us carry out the exclusive formation of a desired single product.
Positive sign in the average rate of the reaction signifies the formation of the species in consideration through the course of the reaction.
While the negative sign in the average rate signifies the decrease in concentration of the species in consideration through the course of the reaction.

Note:
The rate law is an experimentally determined quantity and can be used to predict the relationship between the concentrations of reactants and the rate of the reaction. For elementary reactions, the rate equation can be simply derived from first principles using the collision theory. The rate equation of a reaction with a multi-step mechanism cannot be calculated from the stoichiometric coefficients of the overall reaction.