Branch Of Chemistry Dealing With Study Of Reaction Rates

Chemical kinematics is the branch of chemistry thatdetermined as the speed or velocity with which a
deals with the study of reaction rates or even speedreaction takes place. It can be expressed qualitatively
of reaction and their mechanics. The kinetic studies notas well as quantitatively. The qualitative rate is based
only help us to determine the reaction rates but alsoon certain visual parameters like disappearance of
does describe the conditions by which the reactionreactants, color change, effervescence, etc. the rate
rates can be altered. Besides this the mechanismexpressed as such provides arbitrary conclusions
governing the reactions could also be predicted on theabout the rate of a reaction. Quantitative rate of a
basis of logical kinetic data.chemical reaction provides with much better
During the course of study we all come across a wideinformation about the rate data and the accurate rate
variety of chemical reactions having different rates. Inof a reaction. Quantitatively, the rate of chemical
thermodynamics we studied that the decrease in freereaction may be expressed as the rate of decrease in
energy is quite helpful in predicting the feasibility ofconcentration of any one of the reactants or the rate
chemical reactions. However, knowledge of freeof increase in concentration of any one of the
energy change of reaction does not give us any ideaproducts. Thus the reactions may  be involving same
about the speed or rate of the reaction.stoichiometric coefficients of all the reactants and
So, depending upon the reaction rates, variousproducts like in the case of reaction between nitrogen
reactions can be categorized into three types as verydioxide and carbon monoxide, as the reactants and
fast, very slow or moderately slow. Very fastproducts appear in the same stoichiometric proportions.
reaction’s are those which occur almostSo the rate of the reaction may be expressed in
instantaneously like precipitation of silver chloride whichterms of rate of disappearance of nitrogen dioxide or
occur instantaneously by simply adding aqueouscarbon monoxide or alternatively, by the rate of
solution of sodium chloride to aqueous solution of silverappearance of carbon dioxide or nitric oxide which
nitrate. The rates of such reactions cannot beever may be convenient. In this case the rate of
determined easily. The obvious reason for a very fastreaction can be followed easily by simply measuring
rate of such reaction is that no chemical bonds are tothe change in intensity of color.
be broken among the reactants.If the reactants and products have different
Very slow reactions comprises reactions which occurstoichiometric coefficients, this means that for every
at a very slow rate. These reactions may requiremole of the reactants reacting we get two moles of
month or even years together for their completion likethe products. So the rate of formation of the products
rusting of iron. The rates of such reactions are hardlywill be twice the rate of disappearance of the
of any physical importance. Moderately slow reactionsreactants. So, in order to avoid the difference in the
refer to reactions in between very fast type and verytwo rates, i.e., to get a unique value of the reaction rate
slow type reactions. These reactions proceed atirrespective of the species selected, we simply divide
moderate speed which can be easily measured.the rate of change of concentration by the
Inversion of cane sugar and hydrolysis of starch arestoichiometric coefficient of reactant or product that
common examples of this type of reactions.are involved in the chemical reaction.
The rate of a chemical reaction can also be