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Rate Of Reaction & Catalysts
Noadswood Science, 2012
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Rate Of Reaction & Catalysts
Friday, April 14, 2017 Rate Of Reaction & Catalysts To understand how catalysts affects the rate of reaction
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Rate Of Reaction A variety of factors affect the rate of reaction, including: - Temperature Concentration of a dissolved reactant Pressure of a reacting gas Surface area of reactants Catalysts
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Catalysts For chemical reactions to occur: -
Existing bonds have to begin breaking so that new ones can be formed The molecules have to collide in such a way that the reacting parts of the molecules are brought together Catalysts can help with either or both of these processes
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Catalysts Other catalysts, especially enzymes, absorb molecules in a way that not only stretches bonds but also brings the reacting parts of reactants right next to each other...
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Hydrogen bonds stretched
Catalyst Example In the presence of a nickel catalyst vegetable oil and hydrogen react to form margarine – nickel adsorbs hydrogen gas onto its surface in such a way that the bond holding the hydrogen molecule together becomes stretched This partial breaking of the bond lowers the activation energy making hydrogen more reactive... H Hydrogen bonds stretched H H H H H Ni
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Catalysts Catalysts are used in the manufacture or application of a huge number of products: - Biological soap powder uses biological catalysts (enzymes) Enzymes in pineapple help cooked ham to be more tender Plastics are made using catalysts Manufacture of fertiliser via the Haber Process involves use of an iron catalyst Synthetic materials like polyester are made using a catalyst Catalytic converters in cars – the catalyst encourages decomposition of nitrogen oxide (poisonous) back into nitrogen and oxygen
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Experiment Plan and carry out an experiment investigating how catalysts affects the rate of reaction (record your results)… Get the 3x catalysts: liver; celery; and manganese dioxide Measure 25cm3 hydrogen peroxide into a conical flask with a delivery tube leading to a measuring cylinder submerged in water Add the catalyst and measure the oxygen produced every 10 seconds for 2 minutes Repeat using different catalysts Graph your results and write a conclusion
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Oxygen produced (ml) every 10 seconds
Experiment Catalyst Oxygen produced (ml) every 10 seconds 10 20 30 Etc… Liver Celery Manganese dioxide
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Experiment Why did we not use boiled liver?
The enzymes in the liver (catalysts) would denature (change shape) if the liver was boiled, and would no longer work
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Catalysts Catalysts increase the rate of reaction without being used up – they do this by lowering the activation energy needed With a catalyst, more collisions result in a reaction, so the rate of reaction increases – different reactions need different catalysts Catalysts are important in industry because they reduce costs
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Catalyst Disadvantages
Catalysts can be very expensive to buy, and often need to be removed from the product and cleaned Different reactions also use different catalysts, so if more than one product is made then different catalysts will need to be bought Catalysts can also be ‘poisoned’ by impurities (stopping them working) meaning the reaction mixtures must be kept clean – all of these cost money!
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Summary The rate of a reaction increases if: -
The temperature is increased The concentration of a dissolved reactant is increased The pressure of a reacting gas is increased Solid reactants are broken into smaller pieces A catalyst is used
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Summary For a chemical reaction to occur, the reactant particles must collide – collisions with too little energy do not produce a reaction
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Summary Changing concentration or pressure – if the concentration of a dissolved reactant is increased, or the pressure of a reacting gas is increased: There are more reactant particles in the same volume There is a greater chance of the particles colliding The rate of reaction increases Changing particle size – if a solid reactant is broken into small pieces or ground into a powder: - Its surface area is increased More particles are exposed to the other reactant
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Summary Changing the temperature – if the temperature is increased: -
The reactant particles move more quickly More particles have the activation energy or greater The particles collide more often, and more of the collisions result in a reaction The rate of reaction increases Using a catalyst – catalysts increase the rate of reaction without being used up They do this by lowering the activation energy needed: with a catalyst, more collisions result in a reaction, so the rate of reaction increases Different reactions need different catalysts Catalysts are important in industry because they reduce costs
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