Bacteria 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 Process N 2 (g) + 3 H 2 (g) 2 NH 3 (g) Nitrogen Fixation Conversion of inert N N into the more accessible NH 3 This reaction is in eqilibrium: Changing certain reaction conditions maximizes the yield and makes the reaction faster

Haber Process N 2 (g) + 3 H 2 (g) 2 NH 3 (g) Nitrogen Fixation What makes the reaction faster ? Reaction carried out at 400 o C 200 atm CATALYST But most importantly in the presence of a CATALYST

“ I can do anything you can do better” Synthesize ammonia at room temperature at normal atmospheric pressure using a biological catalyst called nitrogenase Bacteria

Why do some reactions 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 Reaction Like a high jump

Three stages: 1. The Approach 2. The Transition over the Bar 3. The Landing

Stages of a Chemical Reaction A dynamic process of molecular change which accompany changes in energy REACTANTSPRODUCTS REACTANTSTRANSITION STATEPRODUCTS

Stages of a Chemical Reaction TRANSITION STATE

Stages of a Chemical Reaction REACTANTSPRODUCTS REACTANTS TRANSITION STATEPRODUCTS

Stages of a Chemical Reaction REACTANTSPRODUCTSTRANSITION STATE

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? 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 the marathon 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?

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 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 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 Reaction STEP 4: The CO 2 product does not stay bound but is released from the catalytic surface to allow new reactant molecules to bind. If CO 2 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 O 2, which is then also released

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