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.
Molecularity of Reaction:
PCl5 → PCl3 + Cl2
2HI → H2 + I2
2SO2 + O2 → 2SO3
NO + O3 → NO2 + O2
2CO + O2 → 2CO2
2FeCl3 + SnCl2 → SnCl2 + 2FeCl2
Differential and Integrated Rate Laws:
Zero Order Reactions:
For Reaction: A → Product
[A]0-[A]t = k0t
[A]0 = Initial concentration of A
[A]t = Concentration of A at time t.
k0 = Rate constant for zero order reaction.
t1/2 = [A]0/2k
Unit of rate constant = mol dm-3s-1
First Order Reactions:
A → Product
(Δ [A] /A) = -k1Δt
or k1=( 2.303/ t)log ([A]0 / [A]t)
t1/2 = 0.693/k1
Half life is independent of the initial concentration of the reactant for a first order
Units of k1 = s-1
N2O5 → 2NO2 + 1/2O2
Br2 → 2Br
2HNO3 → 2NO + H2O
H2O2→ H2O + 1/2O2
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.
Half – Life of a nth Order Reaction:
kt1/2 = (2n-1-1)/(n-1)[A0]n-1
Where, n = order of reaction ≠1
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.
k1 = fractional yield of B × kav
k2 = fractional yield of C × kav
If k1 > k2 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.
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 k1/k2.
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
Integrating equation (i), we get
k = A exp(-Ea/RT)
Where, k = Rate constant
A = pre-exponential factor
Ea = Activation energy
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 10oC.
μ = Temperature coefficient= k(r+10)/kt
Let temperature coefficient of a reaction be ' μ ' when temperature is raised from T1 to T2; 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
All radioactive decay follow 1st order kinetics
For radioactive decay A →B
-(dNA/dt) =l NA
Where, l = decay constant of reaction
NA = 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: Nt = Noe-lt
Half Life: t1/2= 0.693/λ
Average life time: Life time of a single isolated nucleus, tav= 1/λ
Activity: Rate of decay
A = dNA/dt, Also, At = Aoe-lt
Specific Activity: activity per unit mass of the sample.
Units: dps or Becquerrel