biography of arrhenius

8/6/2019 Biography of Arrhenius

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Biography of Arrhenius

Svante August Arrhenius was born in Vik, Sweden in 1859. At age 25 he turned in his PhDthesis at the University of Uppsala, Sweden. His PhD examining committee did not thinkvery highly of his thesis and rated it 4th class. His oral thesis defense did not fair muchbetter as they rated it as only 3 rd class. Arrhenius left Sweden for five years to work with

Oswald, Boltzmann and van't Hoff. In 1889 his interpretation of temperature-dependentequation by van't Hoff led to the universal accepted Arrhenius equation for kinetic rate lawsin chemistry.

He received the Nobel Prize in 1903. From 1905 until his death in 1927 he was director of Physical Chemistry at the Nobel Institute.

k=Ae-E/RT

The larger the activation energy, the more temperature sensitive k andthus the reaction rate.

Why is there an Activation Energy?

(1) the molecules need energy to distort or stretch their bonds in order

to break them and to thus form new bonds

(2) as the reacting molecules come close together they must overcome both steric and electron repulsion forces in order to react



In our development of collision theory we assumed all molecules had thesame average energy. However, all the molecules don’t have the same

energy, rather there is distribution of energies where some molecules havemore energy than others. The distraction function f(E,T) describes this

distribution of the energies of the molecules. The distribution function isread in conjunction with dE

f(E, T) dE = fraction of molecules with energies between Eand E + dE

One such distribution of energies is in the following figure.



By increasing the temperature we increase the kinetic energy of thereactant molecules which can in turn be transferred to internal energy to

increase the stretching and bending of the bonds causing them to be in anactivated state, vulnerable to bond breaking and reaction.

We see that as the temperature is increased we have greater number of molecules have energies E A or greater and hence the reaction rate will be

greater.

on activation Energy

You can tell the overall reaction order by the units of k

CA -rA Reaction Order Rate Law k

(mol/dm3) (mol/dm3*s) zero -rA = k (mol/dm3*s)

(mol/dm3) (mol/dm3*s) 1st -rA = kCA s-1

(mol/dm3) (mol/dm3*s) 2nd -rA = kCA2 (dm3 /mol*s)

http://www.engin.umich.edu/~cre/course/lectures/three/chap3_insert.htm



The activation energy is a measure of the minimum energy a that thereacting molecules must have in order for the reaction to occur.

The reaction of AB + C to form A + BC is shown above along the reactioncoordinate. One way to think of the reaction coordinate is the lineardistance between the AB molecule for a fixed linear distance between the

AC molecule. At the start of the reaction the AB distance is small and theBC distance is large. As the reaction proceeds, the A–C distance remains

fixed but B moves away for A and closer to C and the energy of systemincreases. At the top of the barrier molecule B is equal distance from A and

C. But as it crosses the barrier it moved close to C to form the BC moleculeand the A molecule alone.

What is the reaction rate law for the reaction if the reaction is

elementary? What is rB? What is rC? Calculate the rates of A, B, and C in a CSTR

where the concentrations are CA = 1.5 mol/dm3

, CB = 9 mol/dm3

and kA = 2(dm3 /mol)(1/2)(1/s). Solution



Let's calculate the rate if,

Then

Examples of Rate Laws

First Order Reactions

(1)

(2)



(3)

(4)

While overall this reaction is first order, it is 1/3 order in

ethylene and 2/3 order in oxygen.

(5)

(6)



(7)

where and

Second Order Reactions

(1)

This reaction is first order in ONCB, first order in ammonia andoverall second order.

(2)

This reaction is first order in CNBr, first order in CH3NH2 and

overall second order.



(3)

with KC = 1.08 and

Nonelementary Reactions

(1)

Cumene Benzene Proplene

(C) (B) (P)

(2)

biography of arrhenius

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