Rate of Reaction:
Order of Reaction
Where m and n may or may not be equal to a & b.
m is order of reaction with respect to A and n is the order of reaction with respect to B.
m + n +… is the overall order of the reaction.
Elementary Reaction:
Molecularity of Reaction:
Chemical Reaction  Molecularity 
PCl_{5 } → PCl_{3} + Cl_{2}  Unimolecular 
2HI → H2 + I_{2}  Bimolecular 
2SO_{2} + O_{2 } → 2SO_{3}  Trimolecular 
NO + O_{3 } → NO_{2} + O_{2}  Bimolecular 
2CO + O_{2} → 2CO_{2}  Trimolecular 
2FeCl_{3} + SnCl_{2} → SnCl_{2} + 2FeCl_{2}  Trimolecular 
Differential and Integrated Rate Laws:
Zero Order Reactions:
For Reaction: A → Product
[A]_{0}[A]_{t } = k_{0}t
Where,
[A]_{0} = Initial concentration of A
[A]_{t} = Concentration of A at time t.
k_{0} = Rate constant for zero order reaction.
Half Life:
t_{1/2} = [A]_{0}/2k
Unit of rate constant = mol dm^{3}s^{1}
Examples:
First Order Reactions:
A → Product
(Δ [A] /A) = k_{1}Δt
or k_{1}=( 2.303/ t)log ([A]_{0} / [A]_{t})
Half Life:
t_{1/2} = 0.693/k_{1}
Half life is independent of the initial concentration of the reactant for a first order
reaction.
Units of k_{1 }= s^{1}
Examples:
N_{2}O_{5} → 2NO_{2} + 1/2O_{2}
Br_{2} → 2Br
2HNO_{3} → 2NO + H_{2}O
H_{2}O_{2}→ H_{2}O + 1/2O_{2}
Pseudo First Order Reactions:
These are the reactions in which more than one species is involved in the rate determining step but still the order of reaction is one.
Examples:
Half – Life of a nth Order Reaction:
kt_{1/2 }= (2^{n1}1)/(n1)[A_{0}]^{n1}
Where, n = order of reaction ≠1
Parallel Reactions:
The reactions in which a substance reacts or decomposes in more than one way are called parallel or side reactions.
If we assume that both of them are first order, we get.
k_{1} = fractional yield of B × k_{av}
k_{2} = fractional yield of C × k_{av}
If k_{1} > k_{2} then
A → B main and
A → C is side reaction
Let after a definite interval x mol/litre of B and y mol/litre of C are formed.
i.e
This means that irrespective of how much time is elapsed, the ratio of concentration of B to that of C from the start (assuming no B and C in the beginning ) is a constant equal to k_{1}/k_{2}.
Sequential Reactions:
This reaction is defined as that reaction which proceeds from reactants to final products through one or more intermediate stages. The overall reaction is a result of several successive or consecutive steps.
A → B → C and so on
…....(i)
…......(ii)
….......(iii)
Integrating equation (i), we get
Arrhenius Equation:
k = A exp(E_{a}/RT)
Where, k = Rate constant
A = preexponential factor
E_{a} = Activation energy
Temperature Coefficient:
The temperature coefficient of a chemical reaction is defined as the ratio of the specific reaction rates of a reaction at two temperature differing by 10^{o}C.
μ = Temperature coefficient= k_{(r+10)}/k_{t}
Let temperature coefficient of a reaction be ' μ ' when temperature is raised from T_{1 }to T_{2}; then the ratio of rate constants or rate may be calculated as
Its value lies generally between 2 and 3.
Collision Theory of Reaction Rate
Radioactivity:
All radioactive decay follow 1^{st} order kinetics
For radioactive decay A →B
(dN_{A}/dt) =l N_{A}
Where, l = decay constant of reaction
N_{A} = number of nuclei of the radioactive substance at the time when rate is calculated.
Arrhenius equation is not valid for radioactive decay.
Integrated Rate Law: N_{t }= N_{o}e^{lt}
Half Life: t_{1/2}= 0.693/λ
Average life time: Life time of a single isolated nucleus, t_{av}= 1/λ
Activity: Rate of decay
A = dN_{A}/dt, Also, At = A_{o}e^{lt}
Specific Activity: activity per unit mass of the sample.
Units: dps or Becquerrel
1. What is chemical kinetics? 
2. How is reaction rate determined in chemical kinetics? 
3. What are the factors that affect the rate of a chemical reaction? 
4. How does temperature affect the rate of a chemical reaction? 
5. What is the role of a catalyst in chemical kinetics? 

Explore Courses for NEET exam
