Chemistry REVISION
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### INTRODUCTION

•color{green} ("Chemical kinetics") :The branch of chemistry which deals with the study of the speeds or the rates of chemical reactions, the factors affecting the rates of the reactions and the mechanism by which the reactions proceed is known as chemical kinetics.

### INSTANTANEOUS AND AVERAGE RATE OF REACTION

r_(av) = (- Delta [R])/(Delta t) = (Delta [P])/(Delta t)

As Deltat → 0 or r_text(inst) = (- d [R])/(dt) = ( d [P])/(dt)

=> For the reaction

5 Br^(-) (aq) +BrO_3^(-) (aq) + 6 H^+ (aq) → 3 Br_2 (aq) +3H_2O (l)

● Rate  = -1/5 ( Delta [Br^-])/(Delta t) = - (Delta [BrO_3^-])/(Deltat t) = - 1/6 (Delta [H^+])/(Deltat) = 1/3 (Delta [Br_2])/(Deltat) = 1/3 (Delta [H_2O])/(Deltat)

•color{green} ("Instantaneous rate of reaction") :The instantaneous rate of reaction,i.e., the rate of reaction at any instant of time is the rate of change of concentration of any one of the reactants or products at that particular instant of time.

### DIFFERENT ORDER REACTIONS

•ZERO ORDER REACTION= [R] = - k t + [R]_0

• FIRST ORDER REACTION= k = (2.303)/t log \ \ ([R]_0)/([R])

### RATE CONSTANT

•color{green} ("Rate constant") :Rate constant may be defined as the rate of the reaction when the molar concentration of each reactant is taken as unity. That is why the rate constant is also called specific reaction rate.

•color{green} ("Order of reaction") :The sum of powers to which the molar concentrations in the rate law equation are raised to express the observed rate of the reaction is called the order of reaction.

•color{green} ("Elementary reaction") :The reactions taking place in one step are called elementary reactions.

•color{green} ("Complex reaction") :When a sequence of elementary reactions (called mechanism) gives us the products, the reactions
are called complex reactions.

•color{green} ("Molecularity of reaction") : The number of reacting species (atoms, ions or molecules) taking part in an elementary reaction, which must collide simultaneously in order to bring about a chemical reaction is called molecularity of a reaction.

•color{green} ("Rate determining step") :The overall rate of the reaction is controlled by the slowest step in a reaction called the rate determining step.

### EFFECT OF TEMPERATURE ON RATE OF REACTION

k = A e^(-E_a//RT)

● A is the Arrhenius factor or the frequency factor. It is also called pre-exponential factor. It is a constant specific to a particular reaction.

● R is gas constant

● E_a is activation energy measured in joules/mole (J mol^( –1)).

•color{green} ("Threshold energy") :The minimum energy which the colliding molecules must have in order that the collision between them may be effective is called threshold energy.

•color{green} ("Activation energy") :The minimum extra amount of energy absorbed by the reactant molecules so their energy becomes equal to threshold value is called activation energy.

•color{green} ("Activated complex") :When the reactant molecules absorb energy, their bonds are are loosened and new loose bonds are formed between them. The intermediate thus formed is called an activated complex or transition state complex.

### CATALYST

•color{green} ("Catalyst") :A catalyst is a substance which alters the rate of a reaction without itself undergoing any permanent chemical change.

### COLLISION THEORY

text(Rate) = PZ_(AB) e^(-E_a // RT)

•color{green} ("Collision frequency") :The number of collisions per second per unit volume of the reaction mixture is known as collision frequency (Z).

•color{green} ("Effective collisions") :The collisions in which molecules collide with sufficient kinetic energy (called threshold energy*) and proper orientation, so as to facilitate breaking of bonds between reacting species and formation of new bonds to form products are called as effective collisions.