Bacteria are Good ChemistsBacteria are Good Chemists

The growth of high-yield crops (e.g., corn) within the United States and other countries depends on the use of nitrogen fertilizers.

Haber ProcessHaber Process

N2(g) + 3 H2(g) 2 NH3(g)

Nitrogen Fixation

Conversion of inert N N

into the more accessible NH3

This reaction is in eqilibrium:

Changing certain reaction conditions

maximizes the yield and makes the reaction faster

Haber ProcessHaber Process

N2(g) + 3 H2(g) 2 NH3(g)

Nitrogen Fixation

What makes the reaction faster ?

Reaction carried out at

400oC

200 atm

But most importantly in the presence of a CATALYSTCATALYST

““I can do anything you can do better”I can do anything you can do better”

Synthesize ammonia at room temperatureat normal atmospheric pressure

using a biological catalyst callednitrogenase

Bacteria

Why do some reactionsWhy do some reactionsnot occur spontaneously?not occur spontaneously?

The lack of spontaneity suggests some kind of an energy barrier

Overcoming the barrier requires an “input” of energy

Process of a Chemical ReactionProcess of a Chemical Reaction

Like a high jump

Three stages:

1. The Approach

2. The Transition over the Bar

3. The Landing

Stages of a Chemical ReactionStages of a Chemical Reaction

A dynamic process of molecular change

which accompany changes in energy

REACTANTS PRODUCTS

REACTANTS TRANSITION STATE PRODUCTS

Stages of a Chemical ReactionStages of a Chemical Reaction

TRANSITION STATE

Stages of a Chemical ReactionStages of a Chemical Reaction

REACTANTS PRODUCTS

REACTANTS TRANSITION STATE PRODUCTS

Stages of a Chemical ReactionStages of a Chemical Reaction

REACTANTS PRODUCTSTRANSITION STATE

C

H

HH

HOC

H

HH

BrHO + + Br

H

C

H H

BrHO

all on the same plane

How does a Catalyst Work?How does a Catalyst Work?

increases the rate of a chemical reaction

by lowering the activation energy

barrier between reactants and products

How does a Catalyst Work?How does a Catalyst Work?

increases the rate of a chemical reaction

by interacting with the transition state structure,

thereby making it more energetically stable.

QUESTION: Paul Tergat from Kenya holds the world record for

the marathon race, with a time of 2 hours, 4 minutes, and 55 seconds (Berlin, 2003).

How quickly would Paul Tergat have completed themarathon if his running rate were increased by (a) a hundred fold, (b) a thousand fold, and (c) a million fold?

How does a Catalytic Converter Work?How does a Catalytic Converter Work?

CO + O2 CO2 + O

carbon monoxide oxygen gas carbon dioxide oxygen atom

The Steps of a Metal-Catalyzed Reaction The Steps of a Metal-Catalyzed Reaction

STEP 1: The catalyst attracts and binds the reactant molecules, where the manner of binding depends on the metal surface and the structure of the molecules. The C≡O molecule binds vertically because it is polar, while the O=O molecule is non-polar and binds horizontally. Some motion on the surface still occurs but the binding restricts the molecules to two-dimensions, effectively concentrating the reactants so they have more chance to collide and react.

The Steps of a Metal-Catalyzed ReactionThe Steps of a Metal-Catalyzed Reaction

STEP 2:

The bonds in the reactants weaken (C≡O) or break (O=O) due to interactions with the metal atoms in the catalyst. Oxygen atoms are normally unstable in isolation, but they are stabilized through interaction with the metal atoms of the catalyst.

The Steps of a Metal-Catalyzed ReactionThe Steps of a Metal-Catalyzed Reaction

STEP 3: An unstable and transient transition state is formed on the reaction pathway, which is distinct from the reactants or the products. The transition state is bound and stabilized by the catalyst more strongly than any other species. The transition state for the metal catalyzed reaction is not identical to that in the gas phase reaction without a catalyst. In essence, the metal catalyst opens up a new chemical pathway through which the reactants can be converted to products.

The Steps of a Metal-Catalyzed ReactionThe Steps of a Metal-Catalyzed Reaction

STEP 4:

The CO2 product does not stay bound but is released from the catalytic surface to allow new reactant molecules to bind. If CO2 remained stuck to the surface, the metal surface would become coated over time and no longer function as a catalyst. The remaining O atom on the surface reacts during the next catalytic cycle to create a molecule of O2, which is then also released

H H CC CCAA

BB

XX

YYH H

H

CC CCAA

BB

XX

YY

H H H

H

H H HCCCC

AABB

XXYY

H

H H HCCCC

AABB

XXYY

H H

H

CCCC

AABB

XXYY

H

H HH

CCCC

AABB

XXYY

H