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Catalysis October 2015 Catalyst Catalysis October 2015 Catalyst

Catalysis October 2015 Catalyst - PowerPoint Presentation

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Catalysis October 2015 Catalyst - PPT Presentation

A substance that speeds up a reaction without being consumed itself How By providing a new pathway for the reaction one with a lower activation energy Catalyzed Reaction Note a greater fraction of the collisions are effective therefore the reaction rate increases ID: 722187

slow reaction step catalyst reaction slow catalyst step bonds rate catalysts activation energy catalyzed reactants heterogeneous phase homogeneous surface uncatalyzed break clo

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Presentation Transcript

Slide1

Catalysis

October 2015Slide2

Catalyst

A substance that speeds up a reaction without being consumed itself

How? By providing a new pathway for the reaction, one with a lower activation energySlide3

Catalyzed Reaction

Note: a greater fraction of the collisions are effective therefore the reaction rate increases

Uncatalyzed

Reaction

Catalyzed ReactionSlide4

Catalysts can be classified as:

Homogeneous – where the catalyst is in the same phase as the reactants

2) Heterogeneous – where the catalyst is in a different phase – usually a solidSlide5

Heterogeneous catalysts

Consider the following reaction:

C

2

H

4

+ H2  C

2H6Slide6

The reaction is slow; most of the activation energy is used to break the strong H-H bondSlide7

The reaction rate can be greatly increased in the presence of:

Platinum

Palladium

NickelSlide8

1) The reactants are adsorbed (loosely attached) onto the surface of the nickel

2)

Ni–H

bonds are formed as H-H bonds breakSlide9

3) Molecules and atoms migrate toward each otherSlide10

4) C-H bonds are formedSlide11

5) The product ethane is released from the surface of the Ni (desorbed)

6)

The Ni

remains unchanged and can be used over and over againSlide12

Homogeneous catalysts

Provide a completely new reaction mechanism that has a faster slow step than the slow step of the

uncatalyzed

reaction

What must be true about the

Ea of the catalyzed mechanism’s slow step?Slide13

Consider the reaction:

2H

2

O

2(l)

 2H2O

(l) + O2(g)

The reaction is very slow

If rate = k[H

2

O

2

]

2

propose a mechanismSlide14

BUT

with a catalyst:

H

2

O

2 + I

-  H2

O + IO-

(slow)

H

2

O

2

+ IO

-

 H

2

O + O

2

+ I

-

(fast

)

What is the catalyst?

What is the reaction intermediate?

What must be true of the activation energy of the slow step?Slide15

Identify the catalyst and reaction intermediate:

Cl

(g)

+ O

3(g)

 ClO

(g) + O

2(g)

O

(g)

+

ClO

(g)

 Cl

(g)

+ O

2(g)