Kinetics - Rate Law Questions

KINETICS - RATE LAW QUESTIONS

2:1. Attempt questions 1 & 2 on pg 361, 3 & 4 on pg 364, 8 on pg 365, 1 on pg 366

2:2 Attempt questions 1 thru 6 on pg 371, #1 (sec 6.2) on pg 371

2:3 Attempt questions #1, 2, 3, 4, & 6 on pg 377

2:4 Attempt questions #2 on pg 390, and #1,3,4 & 5 on pg 397

2:5 A reaction proceeds with the following 2 step mechanism: I) 2 A ® A2 (slow)

a) Identify any catalysts &/or activated complexes? II) A2 + B ® A2B (fast )

b)  Write the eq'n for the overall rx

c)  Write the Rate Law expression

d) What is the effect on the rate if i) [A] is tripled

ii) [B] is doubled

iii) [A] & [B] are both quadroupled

2:6. Another reaction proceeds by the following 3 step mechanism I) A + C ® AC (fast)

II) AC + B ® ABC (fast)

a) Write the eq'n for the overall rx III) ABC + B ® AB2 + C (slow)

b) Write the Rate Law expression

c) What is the effect on the rate if i) [A] x 5

ii) [B] x 0.5

iii) [A] x 0.5 , [B] x 4 , [C] x 0.25

2:7. A reaction occurs between A , B , and C.

i) doubling [A] doubles the rate ii) doubling [B] has no effect iii) doubling [C] increases the rate x 4

* Write the Rate Law Expression for this rx.

2.8. A reaction occurs between P, Q, & R. Experiments to measure the rate produced the following results:

Initial [P] Initial [Q] Initial [R] RATE( mol/L.s)

0.01 0.04 0.10 2 x 10–3

0.03 0.04 0.10 2 x 10–3

0.01 0.12 0.10 18 x 10–3

0.01 0.04 0.30 6 x 10–3

* Write the rate law expression for this reaction and calculate the rate law constant.

2:9. A reaction occurs between X, Y, & Z. The rate law expression is RATE = k [X]2[Z]1/2.

* Calculate numerical values for the rates (a) , (b) & (c) in the chart below.

Initial [X] Initial [Y] Initial [Z] RATE ( mol/L.s ) x 103

0.02 0.10 0.06 4 x 103

0.10 0.10 0.06 a

0.02 0.30 0.06 b

0.02 0.10 0.90 c

2:10. The reaction between nitric oxide and oxygen takes place in two steps: I) NO + O2 ® NO3

a) Write the rate law expression you would expect for this reaction if II) NO3 + NO ® 2 NO2

i) the first step (I) is slower &

ii) the second step (II) is slower

b) Design a rate studies experimental procedure that would verify which step in the above mechanism is the slowest !

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2:11. In the stratosphere there is a very small concentration of oxygen atoms (O). There is also a fairly large amount of ozone (O3 ), which absorbs all but a fraction of the u-v radiation from the sun. Nitric oxide introduced into the stratosphere by man reacts with the ozone in a 2-step rx

I) O3 + NO ® NO2 + O2 (fast)

II) NO2 + O ® NO + O2 (slow)

a) Write the equation for the overall reaction

b) Explain how it is that a small amount of NO can decompose a large amount of O3

c) Write the rate law expression for this reaction

2:12. In basic sol'ns, alkyl bromides (alkyl =R = a hydrocarbon group) are hydrolyzed into alcohols (R-OH) thusly R–Br + OH– ® R–OH + Br– ( R represents any alkyl group )

Two mechanisms below have been proposed for this rx:

1) R–Br ® R+ + Br– (slow) 2) R–Br + OH– ® ( Br–R–OH) – (slow)

R+ + OH– ® R–OH (fast) (Br–R–OH) – ® R–OH + Br– (fast)

a) When methyl bromide (CH3Br) is the reactant the rate varies with [ CH3Br] & [OH–].

i) Which mechanism is this rate consistant with?

ii) What would be the formula of the activated complex ?

b) When tertiary butyl bromide ((CH3)3CBr) is used the rate varies with the concentration of it only.

i) Which mechanism is this rate consistant with?

ii) What would be the formula of the activated complex ?

2:13 The decomposition of SO2Cl2 (SO2Cl2® SO2 + Cl2 ) has a 1st order rate constant of 2.2x10-5 s-1 at 320 °C. If the original concentration of SO2Cl2 is 0.004 M, what will its concentration be (a) after 1 hour and (b) after 1 day?

2:14 The initial dose of a drug in an animal was 25 mg/kg body weight. After 2 h this dropped to 15.0 mg/kg. If this drug is metabolized by a 1st order process, what is the rate constant for this process (min-1).

b) If the drug concentration was 5.0 mg/kg 3.0 hours after ingestion, what was the initial dose of the drug?

2:15 Attempt questions #7, 8, 9, on pg 381

2:16 Strontium-90 has a half life of 28 years. A rock sample was found & analyzed to find only 2% of the expected strontium-90 present. How old is the rock?

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2:18 Which of the letters on the Maxwell-Boltzmann curve and total energy profile diagram label the following.

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2.21.

2:22 Attempt question #3 on pg 391

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2:23 a) On the 1st set of axes below, draw a PE diagram showing b) On the 2nd set of axes below draw a PE diagram for a reaction

a reaction with a ΔHrx=-150kJ/Ea(no catalyst)=120kJ/ with a ΔHrx=50kJ/Ea(no catalyst)=200kJ/Ea (catalyst)=60kJ

Ea (catalyst)=80kJ - Be sure it is fully labelled

2.24 A given reaction mechanism below is known to have 3 separate steps:

i) A + B2 ® AB2 Ea = 4.0 kJ ∆H1 = –10.0 kJ

ii) AB2 + C2 ® ABC + BC Ea = 30.0 kJ ∆H2 = +5.2 kJ

iii) ABC + B2 ® AB2 + BC Ea = 10.0 kJ ∆H3 = –7.8 kJ

a) Write the overall equation for the reaction. Include ∆Hrx

b) Draw a complete energy profile diagram for the entire rx. Roughly draw it to scale and label it fully with all Ea's and ∆H's.

c) Which step is the rate-determining step? Why ?

d) Write the rate law expression for the overall reaction.

2: 25 *OPTIONAL CHALLENGE QUESTIONS

a)  Arrhenius eq’n # 9 on pg 400

b)  Calculating Activation Energies (Ea) using ln(k2/k1) = -Ea/R*(1/T2 - 1/T1)

i)  The reaction of CO2 with water to form carbonic acid has a k=3.75x10-2 s-1 at 25°C and a k=2.1x10-3 at 0°C. What is the activation energy(Ea) for this reaction?

ii)  If a reaction has a k=3.0x10-4 at 25°C and an activation energy of 100 kJ/mol, what will the value of k be at 50°C

2:26 CHAPTER REVIEW QUESTIONS SELF QUIZ on pg 407

#4, 5, 6, 7, 8, 9, 10, 13, *15 & *16 on pg 408/409