1. calcium carbonate (marble) hydrochloric acid carbon dioxide

2. After completing this topic you should be able to : Importance of controlling reaction rate. Learn how chemists control reaction rates by careful consideration of the influence of :  surface area (particle size)  concentration  temperature  pressure  collision geometry

3. "If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied." Richard Feynman (Lectures in Physics) Richard Feynman (Lectures in Physics) Atomic theory

4. Collision theory is a theory proposed independently by Max Trautz in 1916 and William Lewis in 1918, that explains how chemical reactions occur and why reaction rates differ for different reactions William Lewis British chemist (1885 - 1956) and Max Trautz German chemistry (1880 –1960) Collision theory Collision theory is sometimes summarized by the idiom: “You can’t react if you don’t collide.” The collision must provide enough energy to break the bonds in the reactant molecules Then new chemical bonds form to make product molecules.

5. Activation energy and collision geometry When two billiard balls collide, they simply bounce off of each other. This is also the most likely outcome if the reaction between A and B requires a significant disruption or rearrangement of the bonds between their atoms. In order to effectively initiate a reaction, collisions must be sufficiently energetic (kinetic energy) to bring about this bond disruption. This will be discussed in more detail later but for now all you need to know is:

6. Progress of a Reaction time Rate C. Why does the graph curve? A. Where is the reaction the quickest? B. Why does the graph level off? A No more products formed. The concentration of the reactants decrease with time. Reactions can be followed by measuring changes in concentration, mass and volume of reactants and products.

7. Factors that affect rate  In your earlier studies you learned that 4 factors affect the rate of a reaction. List 4 ways to increase the rate of reactions: surface area of a solid reactant. concentration or pressure of a reactant. temperature. presence/absence of a catalyst. Increasing the pressure on a reaction involving reacting gases increases the rate of reaction. Changing the pressure on a reaction which involves only solids or liquids has no effect on the rate.

8. Rates of reaction The rate of reaction can be followed by measuring changes in Concentration Mass Volume of gas produced

9. Measuring reaction rates Average rate of reaction = change in mass of product or reactant time interval Units g s -1 time (s) Change in mass (g) Products Reactants

10. Measuring reaction rates Average rate of reaction = change in volume of product or reactant in time for the change to occur Units cm 3 s -1 time (s) Change in volume (cm 3 ) Products Reactants

11. Measuring reaction rates Average rate of reaction = change in concentration of product or reactant time interval Units mol l -1 s -1 Time (s) Change in concentration (mol l -1 ) Products Reactants

12. Effect of surface area Particle size, the smaller the particles, the greater the surface area, the greater the chance of successful collisions. 4 X 4= 16 cm 2 16x6=96 cm 2 2x2 = 4 cm 2 24 X 8= 192 cm 2 4 X 6= 24 cm 2

13. Rate and Particle Size Only the particles on the surface of a solid can be involved in a collision Crushing a solid increases the surface area more particles are available for collision therefore increased rate of the reaction Higher Chemistry Eric Alan and John Harris

14. Effect of surface area Hydrochloric acid reacts with marble chips (calcium carbonate) 2HCl(aq) + CaCO 3 (s) CaCl 2 (aq) + CO 2 (g) + H 2 O (l)

15. How can we follow the reaction? A gas is produced. What will happen to the gas if there is no lid on the container? What will happen to the mass? How can we follow the rate?

16. What to do You are going to follow the rate of the reaction by Measuring the volume of gases produced over time Measuring the loss of mass over time

17. Measuring rate of reaction Two common ways: 1) Measure how fast the products are formed 2) Measure how fast the reactants are used up

18. How can we follow the reaction? If we use a container fitted with a delivery tube we could measure the amount of gas produced. How?

19. What to do - Group 1 Measure 25 cm 3 of 2 mol l -1 HCl into a conical flask fitted with a stopper and a delivery tube Set up an inverted measuring cylinder of water to collect the gas Add 2g marble chips to the acid Measure the volume of gas every 10 seconds Repeat with 2g crushed marble chips

20. To change the concentration of a solution (hydrochloric acid), the solution has to be mixed with different volumes of water. HYDROCHLORIC ACID 2 mol l -1 The following shows how to dilute 2 mol l -1 hydrochloric acid to make 100 cm 3 of lower concentrations. HYDROCHLORIC ACID 1 mol l -1 HYDROCHLORIC ACID 0.5 mol l -1 HYDROCHLORIC ACID 1.5 mol l -1 50 cm 3 2 mol l -1 acid + 50 cm 3 water 25 cm 3 2 mol l -1 acid + 75 cm 3 water 75 cm 3 2 mol l -1 acid + 25 cm 3 water water acid ¾ concentration ½ concentration ¼ concentration

21. What to do - Group 1 Record your results in a table. Plot a graph of volume vs time using the same axes for both sets of data rate = change in volume ( the unit is cm 3 s -1 ) time interval Calculate the rate for the 1 st and 2 nd 25 seconds for each set of results

22. What to do – Group 2 Weigh out 15 g marble chips Measure 25 cm 3 1 mol l -1 HCl into a conical flask Place on balance and zero it Add 2g marble chips to the boat. Now add it to the acid and take mass readings every 10 seconds Repeat using crushed chips

23. What to do – Group 2 Record your results in a the table. Plot a graph of volume vs time using the same axes for both sets of data rate = change in mass ( the unit is g s-1) time interval Calculate the rate for the 1 st and 2 nd 25 seconds for each set of results

24. Swap results Each group should have a sets of results which can be used to plot graphs.

25. time (s)01020304050607080 volume (cm 3 ) C volume (cm 3 ) G Method A results Plot the results on a graph with time on the x axis and volume on the y. Use the same set of axes for both sets of results. 0 14 26 36 44 50 50 50 50 0 22 40 48 50 50 50 50 50 Sample results

26. Rate over 1 st 25 seconds (cm 3 s -1 ) rate over 2 nd 25seconds (cm 3 s -1 ) Whole chips (C) 32-0 25-0 =1.3 50-32 50-25 =0.72 Ground chips (G) 45-0 25-0 =1.8 50-45 50-25 =0.2 Work out the rate of reaction over the first 25 seconds and the second 25 seconds using the formula rate = change in volume = _____________ cm 3 s -1 time interval Time (s) Volume of gas cm 3

27. Method B results Plot the results on a graph with time on the x axis and mass on the y. Use the same set of axes for both sets of results. time (s)020406080100120140160 Mass (g) C mass(g) G 2.0 1.4 1.0 0.7 0.5 0.35 0.3 0.25 0.25 2.0 0.7 0.4 0.3 0.25 0.25 0.25 0.25 0.25 Sample results

28. Work out the rate of reaction over the first 25 seconds and the second 25 seconds using the formula rate = change in mass The answer will have the units g s -1 time interval Rate over 1 st 25 seconds (g s -1 ) rate over 2 nd 25seconds (g s -1 ) Whole chips (C) 0.8-2 25-0 =0.05 0.35 -0.8 50-25 =0.018 Ground chips (G) 0.3-2 25-0 =0.068 0.25-0.3 50-25 =1x10 -3 Loss in mass (g) Time (s)