Section 16'4: Integrated rate laws

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Section 16.4 Integrated rate laws
Example At 1000 ºC, cyclobutane (C4H8)
decomposes in a first-order reaction, with The
very high rate constant of 87 s-1, to two
molecules of ethylene (C2H4). If the initial
cyclobutane concentration is 2.00 M, what is the
concentration after 0.010 s? What fraction of
cyclobutane has decomposed in this time?
At 25 ºC, hydrogen iodide breaks down very slowly
to hydrogen and iodine rate kHI2 The rate
constant at 25 ºC is 2.4 x 10-21 L/mol sec. If
0.0100 mol of HI(g) is placed in a 1.0 L
container, how long will it take for the
concentration of HI to reach 0.00900 mol/L?
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Section 16.1 to 16.4 Solving Rate Problems A
Summary
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Section 16.4 Integrated rate laws (continued)
What if you have concentration and time data, but
do NOT have the rate law (rate kAmBn) or
the initial rate data?
Trial-and-error graphical plotting
For zero-order reactions
For first-order reactions
For second-order reactions
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Section 16.4 Integrated rate laws (continued)

Trial-and-error graphical plotting
(Ocean
Acidification!!!)
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Does coral dissolution follow zero-order
kinetics?
Does coral dissolution follow first-order
kinetics?
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Does coral dissolution follow second-order
kinetics?
If coral dissolution followed first-order
kinetics, what would that tell you about the
dependence of the overall reaction rate of CaCO3
dissolution? (What does the rate depend on?)
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Section 16.4 Integrated rate laws (continued)
Example 2 Trial-and-error graphical plotting
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Section 16.4 Integrated rate laws (continued)
Half-life (t1/2)
It is the time required for a reactant
concentration to reach half of its initial value.
Applies to first-order reactions only ?
independent of the starting concentration (In
other words, if independent of starting
concentration ? the t1/2 is independent of the
number of other particle present)
t1/2 0.693 / k
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Section 16.4 Integrated rate laws (continued)
Radioactive decay a common application of
half-life (t1/2)
Carbon-14 t1/2 5568 yrs
How old is the Ice Man? Found in 1991 in the
Alps. (3,330 yrs old)
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Suggested Problems
16.39, 16.41, 16.43 (Answers for these in back of
book)

• What is the average reaction rate, the initial
  reaction rate, and the instantaneous
• reaction rate for the reaction below given the
  data in the Table below?

(2) For the same reaction (above), how would the
reaction rate change if you doubled the H2
concentration? How would you need to change the
O2 concentration if you wanted to quadruple the
reaction rate?
(3) If you know that the rate law for the
reaction shown below is rate kC2H42O3,
then if you doubled the O3, how would the
reaction rate change? How would you need to
Change the C2H4 to quadruple the rxn rate?
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Suggested Problems (Continued)
(4) At 50 ºC, H2Cl2 breaks down into to H2 and
Cl2 gases rate kH2Cl22 The rate constant
1.8 x 10-2 L/mol sec. If 0.40 mol of H2Cl2 is
placed in a 2.5 L container, how long will it
take for the concentration of H2Cl2 to reach 0.25
mol/L?
(5) At 50 ºC, C4H8 decomposes. The rate law is
rate kC4H8. If the concentration
of cyclobutane is 0.80 mol/L after 20 minutes,
what the the rate constant (k) at this
temperature? The initial concentration of
cyclobutane is 1.38 mol/L.
(6) At 700 ºC, H2S gas breaks down into to
diatomic hydrogen and sulfur gases. The rate
kH2S0 If the rate constant is 9.30 x 10-8
mol/L sec and the initial concentration of H2S
gas is 0.18 mol/L, what will be the concentration
of this gas 1 minute after the reaction is
started?