1. Rates of reaction- The effects of a Catalyst and surface area Starter Complete section 1 and 2 of the worksheet

2. Rates of reaction- The effects of a Catalyst and surface area To know the effects of catalyst and surface area on rate of reaction. T be able o explain the effects of factors on rates of reaction in terms of collision theory. To be able to interpret graphs of rate of reaction.

3. Catalyst Warning careful with the wording Speeds up the rate of reaction But remains chemically un changed

4. Why are enzymes so specific? Enzymes are very specific about which reactions they catalyze. Only molecules with exactly the right shape will bind to the enzyme and react. These are the reactant, or substrate, molecules. The part of the enzyme to which the reactant binds is called the active site. This is a very specific shape and the most important part of the enzyme.

5. What happens at the active site? In the same way that a key fits into a lock, so a substrate is thought to fit into an enzyme’s active site. The enzyme is the lock, and the reactant is the key. enzyme reactant + enzyme–reactant complex ↔ products enzyme + ↔ + ↔↔ +

6. The lock and key model

7. Why do enzymes speed up reactions? Enzymes speed up reactions by lowering the activation energy (E a ) of a reaction. The activation energy is the energy needed to start a reaction. Different reactions have different activation energies. reaction (time) energy (kJ) E a with enzyme E a without enzyme

8. Factors affecting enzymes The rate of enzyme-catalyzed reactions depends on several factors. What are some of these? All enzymes work best at only one particular temperature and pH: this is called the optimum. Factors that affect the rate of a reaction include: substrate concentration temperature Different enzymes have different optimum temperatures and pH values. pH enzyme concentration surface area pressure.

9. Factors affecting enzymes If the temperature and pH changes sufficiently beyond an enzyme’s optimum, the shape of the enzyme irreversibly changes. normal denatured heat pH This affects the shape of the active site and means that the enzyme will no longer work. When this happens the enzyme is denatured.

10. 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. Enzymes are proteins made by cells to act as biological catalysts. Catalysts Used in biological detergents (from bacteria grown in tanks which are then removed) Digestion Too high temperature enzymes get denatured Enzymes also work best at a specific pH (you can denature it by adding acid or alkali)

11. Catalyst in Industry Often transition elements or their oxides If the rate of reaction is faster you will get more product in less time You may also be able to reduce pressure and temperature because…….

12. 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 Bond stretched The stretching of the H-H bond lowers the activation energy and helps hydrogen react with the oil Ni catalyst Catalysts

13. New bonds form Old bonds start to break Scientific theory Chemical reactions involve the formation of bonds between atoms but often before new bonds can be formed old ones have to be broken. activation energyThis means that there has to be enough energy (activation energy)to start breaking the old bonds before a reaction can occur. Reactants When a catalyst is present the reactants are able to react in a way that requires less energy. This means in a set time more collisions will be successful.

14. 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 Bond stretched The stretching of the H-H bond lowers the activation energy and helps hydrogen react with the oil Ni catalyst Catalysts

15. Catalyst 1.Sketch graph 2.What does activation energy mean ? 3. What is wrong with this statement “a catalyst lowers the activation energy”. Progress of reaction

16. Catalyst Alex investigated a reaction, the reaction produced a gas. Alex wanted to know if x, y or Z were catalysts for the reaction. He repeated his experiment under exactly the same conditions nut each time added a small amount of X, Y or Z. In each case he timed how long it took for the reaction to finish. The results are shown in the table. State if each of X, Y and Z acted as a catalyst and give reasons for your answer. Substance addedTime (s) None167 X156 Y169 z8

18. Rates of reaction-Surface area Aims. C-To know how surface area affects rate of reaction B-to use collision theory to explain the rate of reaction and particle size A-To plot rates of reaction and calculate rate of reaction from a graph.

19. C-to use key words surface area to describe rate of reaction using large and small particles. Which reaction is faster ? If reactants have the SAME MASS AB Smaller particlesLarger particles

20. Surface area The reactions of solids can clearly only take place at the surface of the solid. If we break a solid into smaller pieces we get more area and a faster reaction. Molecules collide with the surface of the solid Extra surface for molecules to collide with.

21. If we grind up a solid to a powder we massively increase the surface area. We therefore massively increase the rate of any reaction as there is more area for collisions to happen, so more frequent collisions Very fast Slow Surface area

22. A B An indigestion tablet fizzes in water – but fizzes much faster if it is crushed. Which glass has the crushed tablet? Crushed Solid

23. PLENARY Complete the practical's then complete the factors affecting rates worksheet