Adapted from powerpoint created by Lance Hammell

Chemical Reaction

13.1

Reactant Bonds Broken, Product Bonds Made

NO2 (g) + CO (g) -> NO (g) + CO2 (g)

N

OOO

O OO CC+ +N

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Molecular Collision Theory

Reactants must collide with

a)correct orientation

b)enough energy, Ea

OC

OO

N

OO OCN

Incorrect Orientation

Correct Orientation

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Reaction path for conversion of A + B into ABReaction path for conversion of A + B into AB

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A + B C + D

Exothermic Reaction Endothermic Reaction

The activation energy (Ea) is the minimum amount of energy required to initiate a chemical reaction.

13.4

Lisa R. ArnoldSouth Georgia College

Activation Energy..

..is energy needed so there is enough energy to break reactant bonds.

..is the energy needed to get molecules in the correct orientation.

..is the energy needed to reach the transition state or activated complex

Lisa R. ArnoldSouth Georgia College

7

Activation Energy

The Activation Energy (Ea) determines how fast a reaction occurs, the higher Activation barrier, the slower the reaction rate. The lower the Activation barrier, the faster the reaction

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What are catalysts?

Simply put, catalysts are substances which, when added to a reaction, increase the rate of reaction by providing an alternate reaction pathway with a lower activation energy (Ea).They do this by promoting proper orientation between reacting particles.In biochemistry, catalysts are known as enzymes.

9

Catalyst lowers the activation energy for both forward and reverse reactions.

Activation Energy

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Activation Energy

This means , the catalyst changes the reaction path by lowering its activation energy and consequently the catalyst increases the rate of reaction.

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Why do we need catalysts?

CEBC video

12

Adsorption and Absorption

H H H H H H H H H H H H H H H H H H

H

H

HH

H

HH H

H

H

HH

HH

H

H

H H

H2 absorption palladium hydride

H2 adsorption onpalladium

Surface process bulk process

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Catalytic Converters

One common application for catalysts is for catalytic converters.

Catalytic converters are found in automobiles.

Their role is to reduce to emissions of harmful gases (CO, VOC’s, NOx) that are the result of the combustion of fuel in vehicle engines.

Specifics of Catalytic Converters

Most modern cars are equipped with three-way catalytic converters. "Three-way" refers to the three regulated emissions it helps to reduce -- carbon monoxide, VOCs and NOx molecules.

A: Reduction CatalystB: Oxidation CatalystC: Honeycomb Ceramic Structure

The converter uses two different types of catalysts,

Both types consist of a honeycomb-shaped ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium.

Step 1: The Reduction Catalyst

The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2.The equation for this is as follows:

2 NO => N2 + O2 or 2 NO2 => N2 + 2 O2

Step 2: The Oxidization Catalyst

The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. The equation for this process is as follows:

2 CO + O2 => 2 CO2

Once this process is complete, most of the harmful substances have been broken down into harmless

ones such as N2, O2, and CO2.

Catalytic Converter Summary

Applications of Catalysts

Fuel Cells