Rates of Reaction

1. Rates of Reaction Ali Artani Josh Li-Taylor Lageishon Mohanadas Zachery Oman

2. Introduction • A chemical reaction is the combination of reactants to form a product • Its rate is the speed at which the product forms • There are four main factors that increase the speed of a chemical reaction: • Surface Area • Concentration • Temperature • Catalyst

3. General Theory • All four factors are supported by the Collision Theory: • Reactant particles must collide to have a reaction • In a reaction, existing bonds of reactants are broken and new bonds are formed to create product • At impact there is a certain amount of energy and a proper orientation to do this • If there is not enough energy in impact, there is not enough energy to break bonds, thus can’t make new bonds • Not all collisions have the appropriate requirements

4. Some Key Terms • Activation energy • The minimal energy needed for a successful collision (refer to collision theory) • Transition state • The phase whereby reactants are at the highest level of energy will become products and can not revert back

5. Surface Area Summary Greater surface area  Faster reaction A reaction takes place only if the particles in the liquid or gas collide with the particles in the solid And… Increasing the surface area of the solid means more particles of one reactant are exposed to the other, which increases the chances of collisions taking place Thus… A higher rate of reaction!

7. Surface Area Common Examples Powdered drinks: Kool-Aid, Gatorade, hot chocolate, etc.  Sometimes we get chunks! Sugar cubes VS. Fine sugar Which will generally dissolve first?

8. Surface Area Surface Area Experiment Large, medium, and powdered crystals of CuSO4 were dissolved in water to see which ones would take the shortest and longest time to dissolve. What do you think happened? *** mass of CuSO4, volume of water, SATP conditions all constant for all three tests Condition of CuSO4 (crystallized) Large crystal chunks Medium sized crystals Fine powder Time to Dissolve in water (in minutes) 4:56.5 0:37.98 0:04.78

9. Concentration Summary Stronger concentration  Faster reaction Reactants have a certain amount of molecules (particles) in proportion to the mass or volume of the reactant By… Increasing the concentration of a reactant, we will be increasing the amount of particles while keeping the same mass/volume of the same reactant, which increases the numbers of chances collision can take place Thus… A higher rate of reaction!

10. Concentration Common Examples • Concentrated soft drinks • Reduced shipping costs (e.g. syrup boxes that are used in fountain drink machines where water is added to create drink) • Beer with 2.5% vs. 5%, etc. • Affects senses more • Concentrated Detergent

11. Concentration Concentration Experiment • Mark white paper with X • Dissolve 2g of crystallized Na2S2O35H2O into 10mL of H20 • Pour 10mL HCl 4M into beaker • Time how long it takes for cloudy solution to block visual of X • Repeat using concentrations of 2M, 1M, and 0.5M of 10mL of HCl

12. Concentration Results

13. Temperature Summary Stronger temperature  Faster reaction When reactants react with each other or an experiment is done, it is done at a certain temperature (usually room temperature) By… Adding heat to the combining reactants will increase the space in between particles and increase the speed of reactants particles by giving them energy. (Look at Particle Theory) Thus… Increasing the amount of successful collisions because it gives some particles that would normally have energy below the activation level to have enough energy for a successful collision, meaning a higher rate of reaction!

14. Temperature Diagram • This is the Maxwell-Boltzmann distribution diagram (aka energy profile diagram) • It shows the proportion of particles that can have successful and non-successful collisions • This is how it looks without trying to speed up the reaction

15. Temperature • Let T = the original graph, t = temperature increase • Does not gain or lost particles, but changes the ratio of successful vs. non-successful collisions • Temperature increases the reaction rate by changing reactants itself rather then physically altering the reactants like concentration and surface area

16. Temperature Common Examples: • Heating frozen leftovers vs. leftovers that have warmed up on the counter • Dunking cookies in hot coffee or cold milk • Making instant coffee in cold water or preheated water

17. Temperature Temperature Experiment • Similar method as of concentration experiment • Only 1M HCl used however • And three different solutions of Na2S2O35H2O used; one room temp, one heated at medium and another at max heat for 1 minute each

18. Temperature Results

19. Catalyst Summary Adding a catalyst  Faster reaction When reactants combine their particles must fulfill certain requirements to have a successful reaction By… Adding a catalyst, it will create an alternative pathway that the chemical reaction will follow, without being engulfed or added to the reaction. On this alternative route, the catalyst manipulates the activation energy level and the level to reach the transition state and lower the requirements Thus… Increasing the amount of particles with enough energy to have a successful collision on this alternative pathway without changing the number of particles in the reactants, meaning a higher rate of reaction!

20. Recognize this from anywhere?

21. Catalyst • Once again, does not gain or lose particles but changes the ratio of successful vs. non- successful collisions with the use of an alternative route • Similar to temperature, this type of catalysts does not change the reactants psychically • Unlike temperature, this catalyst does not change the reactants at all but lowers the requirements on this alternative pathway

22. Catalyst • Also! (Other Graphs) • The words alternative route are key • There are different types of Catalysts

23. Catalyst Catalyst Experiment • Mix 3mL KMnO4 with 1mL H2SO4 to create an acidic medium • Mix the product of the previous with 5mL Na2S2O35H2O • Record results under three conditions: • At SATP with no additional enhancers • Heat to a minimum of 70C • Place MnSO4 in the product

24. Catalyst Results Room temp: Reacted Substance:

25. FIN QUESTIONS?