Kinetics: Integrated Rate Laws Lecture 23
Jun 23, 2015
Kinetics: Integrated Rate Laws
Lecture 23
Integrated rate laws
A sample problem
on determining reactant concentration at a given
time.
If we obtain a straight line,
when we plot ln[reactant] vs time, the reaction is first order with respect to that reactant.when we plot 1/ [reactant] vs time, the reaction is second order with respect to that reactant.when we plot [reactant] vs time, the reaction is zero order with respect to that reactant.
Graphical determination of the reaction order: look for a straight line
The half-life (t1/2) of a reaction
is the time required for the reactant
concentration to reach half of its initial
value.
The half-life of a first order reaction
ln([A]0/[A]t)=kt
ln([A]0/0.5[A]0)=kt1/2
ln2=kt1/2 , 0.693=kt1/2
t1/2 = ln2/k = 0.693/k
Half-life in a first order process
In the radioactive decay of elements,decomposition of each
particle in a first order process is independent of the number of particles.
The half-life of a second order reaction
1/[A]t — 1/[A0] = kt
1/0.5[A]0 — 1/[A0] = kt1/2
2/[A]0 — 1/[A0] = kt1/2
1/[A0] = kt1/2
t1/2=1/k[A0]
Half-life in a second order process
The half-life of a zero order reaction
[A]t — [A]0 = —kt0.5[A]0 — [A0] = —kt1/2
—0.5[A]0 = —kt1/2
0.5[A]0 = kt1/2
[A]0 = 2kt1/2
t1/2= [A]0/2k
Half-life in a zero order process
The half-life and reaction order
The half-life of a first-order reaction is a constant, independent of reactant concentration.The half-life of a second-order reaction is inversely proportional to the initial reactant concentration.The half-life of a zero-order reaction is directly proportional to the initial reactant concentration.
A sample problem
on determining the half-life of a first-
order reaction.
THE END