Definitions Rate of reactions

1. DefinitionsRate of reactions

2. Rates of Reactions Exam Q (Hons) 2003 Q7 2004 Q8 2007/Q9 2011 /Q5 • The rate of reaction is • the changein concentration • per unit time of any one reactant or product.

3. Factors affecting rate • nature of reactants • particle size • concentration • temperature • catalysts

4. Equations to know • Write each equation then check • Decomposition of hydrogen peroxide using manganese dioxide as catalyst MnO2 • 2H2O22H2O + O2 • Sodium thiosulfate and hydrochloric acid • Na2S2O7 + 2HCl  S + 2NaCl + SO2 +H2O

5. Rate Graphs • Concentration v. ( 1 /Time ) • or • Temp v. ( 1 /Time ) • ( 1 /Time )used as Rate and Time inversely related • (shorter time means faster rate) • be careful with units of 1/time

6. Catalyst Exam Q (Hons) 2003 Q7 ‘07/Q9 • is a substance that alters the rate of reaction • but is not consumed in the reaction.

7. Homogeneous catalysis • occurs when the reactants and the catalyst are in the samephase. • example =? liquids • KI catalyses 2H2O22H2O + O2(iodine snake) • And any enzyme

8. Heterogeneous catalysis Exam Q (Hons) ‘07/Q4 • occurs when the reactants and the catalyst are in differentphases. (NB must be phases not states) • example = ? • Al2O3(solid)catalyses • ethanol (gas) ethene Methanol  methanal using platinum

9. Autocatalysis • occurs when one of the products of the reaction catalyses the reaction. • Example = ? • Mn2+ ions in KMnO4 titrations (purple changes to colourless more quickly as titration proceeds)

10. Mechanism of Catalysis • Intermediate Formation theory • Surface Adsorption theory • Know details of each and evidence of intermediate formation theory

11. Enzymes • Are biological catalysts made of protein • Examples of homogeneous catalysis • Need to know 2 examples • Amylase catalyses conversion of starch to maltose • Catalase catalyses conversion of hydrogen peroxide to hydrogen and water

12. Learning Check • Do I know Definition for • Rate of reaction • Catalyst • Homogeneous catalysis • Heterogeneous catalysis • Auto catalysis • Two mechanisms of catalysis Press enter to continue

13. Catalytic converter • Catalysts = ? • Pt + Pd + Rh on honeycomb surface (ceramic) • Gases in CO NO NO2 hydrocarbons • Gases out CO2 and N2 and H20

14. Learning Check • Do I know • 3 metals in Catalytic converter • 4 wastes in exhaust fumes • Problem of each • What each is converted to • What poisons catalytic converter • Type of catalysis occuring in catalytic converter Press enter to continue

15. Collision Theory • for a reaction to occur the reacting particles must collide with each other • a collision only results in a product being formed if a certain minimum energy is exceeded (called activation energy)

16. Effective Collision • Is one in which a reaction occurs • The activation energy has been reached or exceeded. Exam Q (Hons) 2009 Q9

17. Activation Energy • is the minimum energy which colliding particles must have for a reaction to occur (minimum energy required for effective collisions between particles) Exam Q (Hons) 2006/Q7 2009/Q9

18. Activation Energy 2 • Catalysts lower the activation energy of a reaction Compare E act Without catalyst with catalyst

19. Energy Profile Diagram • Sketch an energy profile diagram for an endothermic reaction. • Press enter when ready and • It should look like this

20. EndothermicEnergy Profile Diagram Products Activation Energy Energy In Reactants Note – axes should be labelled Time (x) and energy (y) Curve should be smooth !

21. Energy Profile Diagram • Sketch an energy profile diagram for an exothermic reaction. • Press enter when ready and • It should look like this

22. ExothermicEnergy Profile Diagram Activation Energy Reactants Energy Out Products Note – axes should be labelled Time (x) and energy (y) Curve should be smooth !

23. Learning Check • Do I know Definition for • Effective collision • Activation energy • Can I draw energy profile diagram for • Exothermic reaction • Endothermic reaction • Either of above with catalyst The End