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Definitions Rate of reactions

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Presentation on theme: "Definitions Rate of reactions"— Presentation transcript:

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


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