Chemical Kinetics
             Chemical kinetics is a most important part of chemistry through which we know about the rate chemical reactions, the mechanism by which they take place and the factors which influence the rate.
Types of reactions:
Instantaneous reactions: these are the reactions which are complete in a fraction of seconds. Such are generally ionic reaction.
                 NaCl (aq) +AgNO3 (aq) ž AgCl (s) + NaNO3
Moderate reactions: These are the reactions which take a very long time to complete. The rate of such reaction can be conveniently measured.       
              CH3COOC2H5 + NaOH žCH3COONa + C2H5OH
Slow reactions: These are the reaction which takes place very long time to complete. The rate of such reactions cannot be measured.
                 Fe +H2O +CO2 ž Fe(OH) (HCO3)
why rate of reaction is differ
The difference in the rates of reactions is due to the different bond energies of reactant and product species. We know that reactants with weaker bonds get readily converted into products because only small amount of activation energy is required such reactions will proceed at a faster rate. But the reactant with stronger bonds requires high activation energy and thus reactions proceed at slow rate.
Rate of reactions
The quantity of a reactant species consumed or the quantity  of a product species formed in unit in a chemical reactions is called the rate of reaction.
Consider a reaction                           AžB
Rate of reaction (r) = amount of A consumed /time taken
Or
Rate of reaction(r) = Amount of B produced /time taken
Average rate of reactions
It is defined as the rate of change of concentration per unit time.
Average rate = change of concentration in given time / time taken
Or
Average rate= ∆(x)/∆t
The expression does not give the true of chemical reaction. The reason is that the rate of a reaction is not constant but changes with time as the time passes, the molar conc. Of reactant goes on decreasing. Due to this, the rate of reaction decreases every moment.
Instantaneous rate
It is defined as the decrease in molar conc. of one of the reactant or increase in molar concentration of any of the product species at a particular instance at a given temperature.
In such case,              ∆x/∆t    is written as dx/dt
Thus the rate of reaction  is defined as the change of concentration of any one of the reactants or products at a particular instant.
Specific reaction rate or rate constant: the proportionality constant in the rate equation is called the rate constant or specific reaction rate.



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