Matriculation Chemistry reaction Kinetics part 5.pdf

8/12/2019 Matriculation Chemistry reaction Kinetics part 5.pdf

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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


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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


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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


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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)


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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


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Distribution of Kinetic Energies of Molecules

Represent total numer of molecules

with +inetic energy greater than !a


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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


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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


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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


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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


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-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 +

=

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Matriculation Chemistry reaction Kinetics part 5.pdf