1. Rates of Reaction In this unit you will investigate what makes chemical reactions go faster. At the end of the unit you will have a 2 hour practical test. This test assesses the Achievement Standard Science 1.1 “Carry out a practical investigation” (4 credits).

2. Chemical Reactions Chemical reactions occur when the reactant particles collide with the right orientation and sufficient energy. How fast a reaction occurs (the rate of a reaction) depends on the number of successful collisions per second. Four factors affect the rate of a reaction ::

3. Temperature Reaction : Marble chips with acid

4. Normal High Temperature Lower Temperature

5. Temperature –The higher the temperature the faster reactant particles move i.e. they have more energy. Therefore there are more collisions and with greater energy.

6. HCl Low Temperature Marbl e Bang! Is it an effective collision? Maybe ?

7. HCl Middle Temperature Marbl e Bang! Is it an effective collision? Probably!

8. HCl High Temperature Marbl e Bang! Is it an effective collision? Definitely !

9. Effect of Temperature Increase in Frequency of collisions AND Increase in energy of collisions

10. Marble Chips Marble Powder Large Marble Chunks

11. Surface Area –The greater the surface area of the reactants the greater the possible number of collisions between reactant particles. –The surface area of solid reactants can be increased by breaking into smaller pieces. –Reactant chemicals are often dissolved in solution. This makes the particles more mobile and so more likely to collide and therefore react.

12. HCl Large Chunks Of Marble Marbl e Bang! Is it or is it not an effective collision? Only on the outside

13. HCl Marble Chips Around the outside of each chip Marbl e Bang! Is it or is it not an effective collision?

14. HCl Marble Powder Very fast with every tiny particle Marbl e Bang! Is it or is it not an effective collision?

15. Effect of Surface Area Increase in Frequency of collisions NO Increase in energy of collisions

16. Bench Acid Strong Acid Dilute Acid

17. Concentration –In a solution that has high concentration there are many reactant particles per mL of solution. Therefore there are more chances for reactant particles to collide. Increasing the concentration increases the rate of reaction. –The concentration of laboratory solutions is measured in moles per Litre (mol L -1 ).

18. HCl Concentrated Acid Marbl e Yes from all angles HCl Bang! Is it or is it not an effective collision?

19. HCl Normal “bench” Acid Marbl e Yes from most angles HCl Bang! Is it or is it not an effective collision?

20. Dilute Acid Marbl e Only occasionally, so very slow Bang! Is it or is it not an effective collision? HCl

21. Catalyst Reaction : Hydrogen Peroxide and the catalyst Potassium dichromate

22. No Catalyst Catalyst

23. Catalysts –A catalyst is a substance that speeds up a chemical reaction without being used up by it. Catalysts speed up reactions by lowering the energy necessary for the reaction to occur. They do this by increasing the proportion of successful collisions through aligning the reactants so they are the correct orientation for the reaction to occur.

24. Effect of Catalyst No Catalyst Catalyst Reactants Products Reaction Progress Energy

25. Effect of Catalyst Decrease in NO effect on frequency of collisions activation energy

26. 1. Purpose of investigation: To investigate how temperature affects the rate of a reaction. 2. Name the key variables in the investigation: Temperature; concentration; surface area; quantity of reactants. 3. Which variable will be changed? Give a suitable range of values for this variable. Temperature: 30 o C, 50 o C, 70 o C. Reactants in water bath monitored with a thermometer. 4. What will have to be measured or observed in order to get some data or information from the investigation? Time taken for solution to go completely colourless. How will it be measured or observed? Clock or stopwatch.

27. 5. What other variables are important in the investigation and will have to be controlled to make it a fair test? Concentration - all solutions will be of known concentrations. The same ‘batch’ will be used throughout the experiment. Surface area-all reactants are in solution. Reactant’s volumes will be measured with measuring cylinders or graduated droppers. Amount of reactant -Volumes will be measured with measuring cylinders. 6. How will you ensure that your results are reliable? Repeat experiment or confer with other class members. Take an average.

28. The Effect of Surface Area On Reaction Rate Experimental Reaction CaCO 3 +2HClCaCl 2 + CO 2 + H 2 O Marble is a naturally occurring mineral and is composed mostly of calcium carbonate. It reacts with acids to form carbon dioxide and water. The rate of this reaction can be measured by timing how long it takes for a certain volume of gas to be produced.

29. 1. Purpose of investigation: To investigate the effect of surface area on reaction rate 2. Name the key variables in the investigation: Temperature; concentration; surface area; quantity of reactants. 3. Which variable will be changed? Give a suitable range of values for this variable. Surface area. Measure 2g quantities of coarse, medium and fine calcium carbonate. 4. What will have to be measured or observed in order to get some data or information from the investigation? Time taken for 20mL of carbon dioxide gas to be collected. How will it be measured or observed? Use downward displacement of gas (see diagram later)

30. 5. What other variables are important in the investigation and will have to be controlled to make it a fair test? Temperature – all carried out at room temp. Concentration – acid will be 1molL -1 for each surface area. Amount of reactant -2g quantities of calcium carbonate measured with a balance. 5mL of hydrochloric acid measured with a measuring cylinder. 6. How will you ensure that your results are reliable? Repeat experiment and take average

31. 8.Use the information from the previous sections to help you write a method for this experiment. Measure 2g of coarse ground calcium carbonate and put into a test tube. Add 5mL of 1 molL -1 hydrochloric acid to a test tube. Collect gas as shown in diagram below. Time how long it takes for 20mL of carbon dioxide gas to be produced. Repeat steps 1-4 for medium and fine ground calcium carbonate. Repeat experiment three times to ensure reliability of results.

32. Present your results and observations in a table. Draw a bar graph of your results. Describe the trend shown by your graph. Write a conclusion giving your interpretation of the results linked to the purpose of the investigation. Explain why surface area affects the rate of the reaction. Evaluate the experiment. This may include: –changes made to method while collecting data, –difficulties or possible sources of error in doing the experiment which effect the reliability of the data collected and validity of the conclusion, –any improvements you would make to the method.

33. Magnesium and Acid – Surface Area Again. Magnesium Magnesium chloride + + hydrochloric acidhydrogen gas Mg+ 2HClMgCl 2 + H 2

34. 1. Purpose of investigation: To investigate the effect of surface area on reaction rate 2. Name the key variables in the investigation: Temperature; concentration; surface area; quantity of reactants. 3. Which variable will be changed? Give a suitable range of values for this variable. Surface area. Measure two 1cm quantities of magnesium. Leave one whole; cut the other into small pieces. 4.What will have to be measured or observed in order to get some data or information from the investigation? Time taken for Mg to dissolve How will it be measured or observed? Stopwatch

35. 5. What other variables are important in the investigation and will have to be controlled to make it a fair test? Temperature – all carried out at room temp. Concentration – acid will be 1molL -1 for each surface area. Amount of reactant -2g quantities of calcium carbonate measured with a balance. 5mL of hydrochloric acid measured with a measuring cylinder. 6. How will you ensure that your results are reliable? Repeat experiment and take average