Kinetics Quick Review

Radioactive Decay and Kinetics

Part II

1 st order ½ life t 1/2=.693/k

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

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

Collision Theory as a Qualitative Explanation of Rate

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

MC Practice

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

Relative Rates

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

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

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

MC

Integrated rate law

Linear equations of integrated rate laws

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

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

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

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

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

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

MC

Catalyst-can be heterogeneous or homogeneous

Temperature versus Activation energy

Arrhenius equation

Graphically determining E a

Arrhenius in free response