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Rates of Reactions – Part 2. Factors affecting the rate of reaction. The surface area The concentration of the reactant The temperature at which the reaction is carried out The use of a catalyst The influence of light. 4. Rate of Reaction – Effect of Catalyst. - PowerPoint PPT Presentation
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Rates of Reactions – Part 2
Factors affecting the rate of reaction
• The surface area• The concentration of the reactant• The temperature at which the reaction is
carried out• The use of a catalyst• The influence of light
4. Rate of Reaction – Effect of Catalyst
Hydrogen peroxide water + oxygen
Powdered manganese IV oxide MnO2 is added as a catalyst.The more finely ground up the manganese oxide is the faster the reaction goes.The mass of the manganese oxide remains the same.It is a catalyst.
Effect of Catalyst
The more catalyst you use the faster the reaction.
The type of catalyst you use will effect the reaction.
Definition of a Catalyst
A catalyst is a substance that increases the rate of a chemical reaction. The
catalyst remains chemically unchanged.
How does a catayst work?
• The provide a surface on which other molecules or atoms can react.
Catalysts in Industry
• Catalysts are very useful as you only need a small amount to dramatically change the rate of a reaction.
• The catalyst is not used up so can be used again and again.
• Used in the production of polythene, painkillers, fertilizers and fabrics.
• The processes to make these compounds, without catalysts, would need much more energy and be much more costly.
Catalytic Convertors
• Used on cars to reduce pollution.• Car exhausts produce CO, NO and
unburnt hydrocarbons.• The catalytic convertor converts
these to less harmful products CO2, N2 and water.
• The catalytic convertor removes polluting oxides and completes the oxidation of unburnt hydrocarbons.
Catalytic Converters Rhodium and platinum – precious metals used
Biological Catalysts
• Living cells also produce catalysts, these are protein molecules called enyzmes.
• Characteristics;– Enzymes are proteins– Very specific – control only one reaction– Temperature sensitive – stop working above 45oC– pH sensitive – work best at pH 7
Enzymes in Industry
• Biological washing powders use enzymes to remove biological stains (sweat, blood, food).
• The enzymes break down protiens and fats.
• Because the enzymes are temperature dependent they need a wash of no more than 40oC
Surface Catalysts and Collision Theory
• One main type of catalyst works by absorbing the reactant molecules onto a solid surface.
• This process of adsorption brings the reacting molecules closer together.
Nickel Catalyzed Hydrogenation
• Finely divided nickel is used as a catalyst to add hydrogen to unsaturated hydrocarbons.
Collision Theory
• If a reaction only occurs when particles collide with the surface of a solid….– Then it follows that the more surface area you have, the
more collisions you have, the faster the reaction is.• This also applies if;– solutions are more concentrated– Gases are more compressed
• Increasing the temperature increases the speed the particles are moving again increasing the probability of collision.
Activation Energy
• Not every collision produces a reaction.
• A certain amount of energy needs to be present to break the bonds, EA
• A catalyst increases the rate of reaction by reducing the EA
Activity
• Page 216• Exercise 7.4 on worksheet• Read about photochemical reactions and do
questions on page 218
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