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 Rate Of Reaction & Catalysts Noadswood Science, 2012.

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Presentation on theme: " Rate Of Reaction & Catalysts Noadswood Science, 2012."— Presentation transcript:

1  Rate Of Reaction & Catalysts Noadswood Science, 2012

2 Saturday, May 02, 2015  To understand how catalysts affects the rate of reaction

3 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

4 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

5 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...

6 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 H H H H H H H H H H H Ni Hydrogen bonds stretched

7 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

8 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 25cm 3 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

9 Experiment Catalyst Oxygen produced (ml) every 10 seconds 102030Etc… Liver Celery Manganese dioxide

10 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

11 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

12 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!

13 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

14 Summary  For a chemical reaction to occur, the reactant particles must collide – collisions with too little energy do not produce a reaction

15 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  There is a greater chance of the particles colliding  The rate of reaction increases

16 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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