biography of arrhenius
Post on 07-Apr-2018
237 Views
Preview:
TRANSCRIPT
8/6/2019 Biography of Arrhenius
http://slidepdf.com/reader/full/biography-of-arrhenius 1/8
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
8/6/2019 Biography of Arrhenius
http://slidepdf.com/reader/full/biography-of-arrhenius 2/8
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.
8/6/2019 Biography of Arrhenius
http://slidepdf.com/reader/full/biography-of-arrhenius 3/8
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)
8/6/2019 Biography of Arrhenius
http://slidepdf.com/reader/full/biography-of-arrhenius 4/8
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
8/6/2019 Biography of Arrhenius
http://slidepdf.com/reader/full/biography-of-arrhenius 5/8
Let's calculate the rate if,
Then
Examples of Rate Laws
First Order Reactions
(1)
(2)
8/6/2019 Biography of Arrhenius
http://slidepdf.com/reader/full/biography-of-arrhenius 6/8
(3)
(4)
While overall this reaction is first order, it is 1/3 order in
ethylene and 2/3 order in oxygen.
(5)
(6)
8/6/2019 Biography of Arrhenius
http://slidepdf.com/reader/full/biography-of-arrhenius 7/8
(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.
top related