matriculation chemistry reaction kinetics part 5.pdf
TRANSCRIPT
-
8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf
1/18
CONCENTRATIONS OF REACTANTS:Reaction rates generally increase as theconcentrations of the reactants are increased.
TEMPERATURE:
Reaction rates generally increase rapidly as
the temperature is increased.
PARTICLE SIZE:
The rate increases as the smaller the size of
reacting particles .
CATALYSTS:
Catalysts speed up reactions.
Factors affecting rate of reaction
-
8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf
2/18
A) CONCENTRATIONS OF REACTANTS
The frequency of collision increases increases with the
concentration
Reaction rate
collision
time
4 particle system
(2 and 2) 4 collision
-
8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf
3/18
A) CONCENTRATIONS OF REACTANTS
A concentration of reactants increases, the frequency
of collision increases.
This would also result in the increase in the quantity of
effective collision. Thus the reaction rate increases.
5 particle system
(3 and 2) 6 collision
-
8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf
4/18
A) CONCENTRATIONS OF REACTANTS
This oservation correlates with the RAT! "A# that has
een previously discussed$
Reaction rate % k& A 'x
& ( 'y
$
(ased on this equation,
(A & B = reactants)(x& y= rate order)
Reaction rate concentration of reactants
REMINDER!)nly in zero order reactions, the rate of reaction is not
dependant upon the concentration of the reactants.
(depending on its rate order)
Reaction rate % k & A '* % k (constant)
-
8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf
5/18
B) TEMPERATURE
As temperature increases, +inetic energy, ofmolecules increases
o, more collisions occur in a given time
Furthermore, the higher the +inetic energy, the
higher the energy of the effective collisions.
o more molecules will have energy greaterthan activation energy, !
a
Thus, the rate of reaction increases
-
8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf
6/18
Distribution of Kinetic Energies of Molecules
Represent total numer of molecules
with +inetic energy greater than !a
-
8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf
7/18
ARRHENIUS EQUATION
-n //0, vante Arrhenius proposed the followingmathematical e1pression for the effect of temperature on
the rate constant, k2
B) TEMPERATURE
k = A e-E aRT
#here$k% rate constant
% constant +nown as the collisionf"#nc$ f%c&oe% natural log e1ponent
Ea% activation energy for the reaction
!% universal gas constant 3/.45 6 mol7879
"% asolute temperature
-
8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf
8/18
ARRHENIUS EQUATION
The relation ship etween the rate constant, kand&'(%can e seen in thek vs T graph2
B) TEMPERATURE
k = A e
-E aRT
#$" (K%#
9
-
8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf
9/18
ARRHENIUS EQUATION DERI*ATION The relationship etween kand Tis clearer when
we further derive the Arrhenius !quation$
B) TEMPERATURE
RT
Ea
Aek
=
).ln(ln RTEa
eAk
=
)ln(lnln RTE
a
eAk
+=
AeRT
Ek
a
lnlnln +
=
ATR
Ek
a ln)(ln +
=.
Natural log both ends
(But ln e = 1)
Thus
See the linear relationship?
y %m x
: C
-
8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf
10/18
raph !epresentation "# The Arrhenius $%uation
;lotting a lnk&s #$"graph would show a clearerrelationship etween k3Rate constant9 and teperature
B) TEMPERATURE
ATR
E
k a
ln)(ln +
=
.
#here,!a% Activation !nergy
R % /.45 6mol787
T % Asolute Temp
A % Collision freq. factor
-
8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf
11/18
-f the value ofA3collision frequency factor9 is not +nown and the same reaction
conducted at two different temperatures.The Arrhenius equation at each temperature
can e written and comined to formed the equation shown in the o1.
B) TEMPERATURE
ATR
E
k
a
ln)(ln +
=.
.
.
Since 'A+is a constant
A
TR
Ek
a ln)(ln +
=