2. Topic 2 - Speed of Reactions

3. Chemical reactions can be fast: Like this explosion

4. Topic 2 - Speed of Reactions Chemical reactions can be slow: Like the decomposition of this apple.

5. Topic 2 - Speed of Reactions Chemical reactions can be very slow: Like the rusting of iron.

6. Topic 2 - Speed of Reactions We can speed up chemical reactions : By increasing the temperature. have more energy move faster collide more often are more likely to react successfully. When heated the particles of substances:-

7. Topic 2 - Speed of Reactions We can speed up chemical reactions: By increasing the concentration. A more concentrated solution has more reacting particles Particles have a bigger chance of coming into contact and reacting.

8. Topic 2 - Speed of Reactions We can speed up chemical reactions: By decreasing the particle size. When a lump of a reacting substance is broken into smaller pieces: the substance can more easily come into contact with the other reactant material from the inside of the lump can now react not just the outside surface.

9. Topic 2 - Speed of Reactions There are many examples of reactions which are affected by temperature. Glucose reacts more quickly with Benedict’s solution as the temperature is increased. Rusting of ships sunk in deep cold waters takes place very slowly. Decay of food speeds up when it is removed from the fridge into a higher temperature. Stains are more easily removed from washing at higher temperatures.

10. Topic 2 - Speed of Reactions There are many examples of reactions which are affected by changing concentration. Clothes can be bleached more quickly using a more concentrated bleach. Magnesium dissolves quicker and gives off hydrogen faster in 2% acid than it does in 1% acid. When the amount of washing powder is less, clothes are not cleaned so effectively because the reaction is slower.

11. Topic 2 - Speed of Reactions There are many examples of reactions which are affected by changing particle size. Chalk lumps react with acid much more slowly than chalk powder.

12. Topic 2 - Speed of Reactions Potatoes cut into smaller pieces cook more quickly than whole potatoes. Smaller particle size speeds up reaction.

13. Topic 2 - Speed of Reactions Iron powder blown into a flame burns rapidly while an iron bar just glows. Large surface area - quick reaction

14. Topic 2 - Speed of Reactions Catalysts Speed up chemical reactions Are not used up in the reaction Can be recovered at the end of the reaction. Save energy because they allow many reactions to be carried out at a lower temperature.

15. Topic 2 - Speed of Reactions Catalysts have many uses: Iron is used as a catalyst in the production of ammonia, an important chemical used in fertiliser production. Nickel is used in hydrogenation of vegetable oils. This process hardens oils to make margarine. Note: the catalysts above are transition metals.

16. Topic 2 - Speed of Reactions Platinum is used in catalytic converters in car exhausts to speed up the breakdown of harmful gases into harmless gases. Platinum is used in catalytic converters in car exhausts to speed up the breakdown of harmful gases into harmless gases.

17. Topic 2 - Speed of Reactions Enzymes are biological catalysts speed up reactions in living things. In the human body reactions have to take place at 37 0 C and many are helped by enzymes. Amylase is an enzyme in our saliva which speeds up the breakdown of starch. Enzymes are used in the production of beer, wine, cheese and yoghurt.