1. Definitions Rate of reactions

2. Rates of Reactions The rate of reaction is the change in concentration
Exam Q (Hons)
2003 Q7
2004 Q8
2007/Q9
2011 /Q5
The rate of reaction is
the change in 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 is a substance that alters the rate of reaction
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 same phase.
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 different phases.
(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
Exam Q (Hons)
2009 Q9
Is one in which a reaction occurs
The activation energy has been reached or exceeded.

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. Endothermic Energy 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. Exothermic Energy 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