1. Rate Of Reaction & Catalysts
Noadswood Science, 2012

2. Rate Of Reaction & Catalysts
Friday, April 14, 2017
Rate Of Reaction & Catalysts
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. 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

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 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

9. Oxygen produced (ml) every 10 seconds
Experiment
Catalyst
Oxygen produced (ml) every 10 seconds 10 20 30
Etc…
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

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