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Kinetics Quick Review. Radioactive Decay and Kinetics.

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Presentation on theme: "Kinetics Quick Review. Radioactive Decay and Kinetics."— Presentation transcript:

1 Kinetics Quick Review

2 Radioactive Decay and Kinetics

3 Part II

4 1 st order ½ life t 1/2=.693/k

5 MC The specific rate constant k, for radioactive beryllium-11 is s -1. What mass of a mg sample of beryllium-11 remains after 28 seconds? a mg b mg c mg d mg e mg

6 MC answer The specific rate constant k, for radioactive beryllium-11 is s -1. What mass of a mg sample of beryllium-11 remains after 28 seconds? a mg b mg c mg d mg e mg

7 Collision Theory as a Qualitative Explanation of Rate

8 Remember these factors that affect reaction rate 1.Nature of reactants—physical state…solids versus gas versus (aq) -- also, if BE is high, will react more slowly -- surface area inc= inc rate 2. Concentration 3.Temperature—Inc temp, Inc KE 4. Calatlyst- lower AE

9 MC Practice

10

11 Reaction Rate Decreases with time Measured as  [ ]/  Instantaneous rate measured as tangent to slope of tangent to the curve of the graph of [ ] versus time at a given time

12 Relative Rates

13 Differential rate law Determined by experimentation Rate constant k – Temperature dependent – Determined by experimentation – Units if given units, can determine order of rxn: 0 order M time -1 1st order time -1 2 rd order time -1 M -1 3 rd order time -1 M -2

14 Order of Reaction 0 order rate = k 1 st order rate = k [ ] 2 nd order rate = k [ ] [ ] or rate= k [ ] 2

15 Rate law Differential: Uses “table logic” or algebra to find order Integrated: graph [ ] vs time ln[ ] vs time 1/ [ ] vs time

16 MC

17

18 Integrated rate law

19 Linear equations of integrated rate laws

20 MC A reaction follows the rate law of Rate=k[A] 2. Which of the following plots will give a straight line? a. 1/[A] versus 1/time b. [A] 2 versus time c. 1/[A] versus time d. ln [A] versus time e.[A] versus time

21 MC A reaction follows the rate law of Rate=k[A] 2. Which of the following plots will give a straight line? a. 1/[A] versus 1/time b. [A] 2 versus time c. 1/[A] versus time d. ln [A] versus time e.[A] versus time

22 Reaction Mechanisms Sequence of bond breaking and bond forming steps (elementary steps) that occurs during the conversion of reactants to products Sum of elementary sets is the net reaction Determined by experiment Elementary step Molecularity: unimolecular—1 reactant rate=k[A ] bimolecular- 2 reactants rate= k[A][B]or k[A] 2

23 Reaction Mechanism and Rate determining step Rate determined by the slowest elementary step—which is the rate determining step Reaction intermediate-produced in one steps, consumed in a subsequent step Catalyst- reactant in initial step, produced in subsequent step, is not show in final equation

24 MC The mechanism below has been proposed for the reaction of CHCl 3 with Cl 2 – Step 1 Cl 2 ↔ 2 Cl (g) fast – Step 2 Cl(g) + CHCl 3  CCl 3 (g) + HCl(g) slow – Step 3 CCl 3 (g) + Cl(g)  CCl 4 (g) fast – Which of the following is consistent with the reaction mechanism? a.Rate= k[Cl 2 ] b.Rate= k [CHCl 3 ][Cl 2 ] c.Rate= k [CHCl 3 ] d.Rate= k [CHCl 3 ]/[Cl 2 ] e.Rate= k [CHCl 3 ][Cl 2 ] 1/2

25 MC The mechanism below has been proposed for the reaction of CHCl 3 with Cl 2 – Step 1 Cl 2 ↔ 2 Cl (g) fast – Step 2 Cl(g) + CHCl 3  CCl 3 (g) + HCl(g) slow – Step 3 CCl 3 (g) + Cl(g)  CCl 4 (g) fast – Which of the following is consistent with the reaction mechanism? a.Rate= k[Cl 2 ] b.Rate= k [CHCl 3 ][Cl 2 ] c.Rate= k [CHCl 3 ] d.Rate= k [CHCl 3 ]/[Cl 2 ] e.Rate= k [CHCl 3 ][Cl 2 ] 1/2

26 MC

27

28 Catalyst-can be heterogeneous or homogeneous

29 Temperature versus Activation energy

30 Arrhenius equation

31 Graphically determining E a

32 Arrhenius in free response


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