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Unformatted text preview: —_ l 1 time conc  time 1n [AL = alct + 1n [A]o [A]: = ‘akt + [A10 ' or
expression
ak
log [A]t — —2.303t + log [A]0
In [A]
plot as y [A] or __1._
[A]
103 [A]
——alc
—ak ak
slope (neg slope)
(neg. slope) (pos. slope)
( “" )
2.303
111 [A10
intercept [A]0 or ‘ L
We
105 [A10
tm [_A]_0 0.693 1
2a]: alc ak[A]o Chapter 14 — Kinetics Hdditional Practice Problems 14.26 A hypothetical reaction A —9 products is second
order in A. The halflife of a reaction that was initially 1.66 M
in A is 310 min. What is the value of the rate constant? 14.27 A reaction shows the same halflife regardless of the
starting concentration of the reactant. Is it a ﬁrstorder or a
second—order reaction? $0. In three different experiments the following results
were obtained for the reaction A—> products: [A]() =
1.00 M, rm =‘ 50 min; [Alo = 2.00 M, (1,2 = 25 min;
[Alo = 0.50 M, 1,,2 = 100 min. Write the rate equation for
this reaction and indicate the value of k. 51. Ammonia decomposes on the surface of a hot tung
sten wire. Following are the halflives that were obtained at
1100 °C for different initial concentrations of NH3:
[NH310 = 0.0031 M, [1,2 = 7.6 min; 0.0015 M, 3.7 min;
0.00068 M, 1.7 min. For this decomposition reaction,
what is (a) the order of the reaction; (b) the rate constant k? [14.641 The gasphase reaction of chlorine with carbon
monoxide to form phosgene, Clz(g)+CO(g) —t COCl2(g),
obeys the following rate law: A[COC2]
Al Rate = = k[Clz]"‘[C0] A mechanism involving the following series of steps is con
sistent with the rate law. C12 = 2C1
c1+c0 = coct
c0c1+c1, .= COC11+C1 ._ Assuming that this mechanism is correct, which of the steps
above is the slow, or ratedetennining, step? Explain. Hint: try making each step the slowest step
[rate—det. step] and see what rate law you get
and if it agrees w. the Hip. rate law giuen. Chemistry 12ﬂ125 — Experiment 16 Lab Report Tips 1.For your graphs you can use a computer to do the graphs. If your graphing program does linear regression (least
squares ﬁtting) you can use this to plot your lines as well. Some programs can also draw nice smooth nonlinear
curves. If you do use the best ﬁt produced by the computer you need to include, both on the graph and in your
report, the equation the computer gives you for the straight line. You should also report the correlation coefﬁcient
(usually signiﬁed as R) which gives you some idea about how good the ﬁt is. The closer R is to i1 the better
your ﬁt is to a straight line, i.e. the closer your points are to falling on the straight line (R=il means all your points fall exactly on a straight line). Some programs report a X2 or variance of the ﬁt, which tell you how
good the ﬁt is. Report these if given. If your program can not do a linear regression than just have it plot the points and you draw the “bestﬁt” line. This
means you have to compute the slope yourself. To do this accurately and correctly you need to have the plotting program draw grid lines so it looks something like the graph paper provided in your lab manuals. Having a few
tick marks at 0.5 inch intervals will not be acceptable. For all graphs, whether by hand or computer generated, they should occupy essentially the whole page. In other
words, spread out your axes so your data occupies as much of the graph and page as possible. 2.For the Beer’s Law Graph you will have 4 experimentally determined data points and the 0,0 point. You want to
draw the best straight line through your 4 exp. det. data points while forcing the line to go through the 0,0 point. You probably won’t be able to do this using a linear regression (leastsquares) program as they don’t usually allow
you to force the line through a data point. 3.If you have access to a spreadsheet program use it rather than the computer program in 160 CE. If you use the
computer program you have to adjust your concentrations by a factor of 103 and you have to copy all the data from
the screen onto you report forms. If you use a spreadsheet you can program the columns to do the calculations for
you and then print out the spreadsheet (with the appropriate titles and column headings) as your report form. In
your spreadsheet you will enter your time and absorbance columns and then have the spreadsheet do the appropriate
calculations for you. You should have a separate spreadsheet for each solution, just like the report forms. I’ve
listed below what should go in the other columns of your spreadsheet. You also need to show an example of each
of these calculations in your report. Column 1: time
Column 2: Absorbance (A) Column 3: [Cr(EDTA)‘], = A/m
where, A: absorbance
m: slope of Beer’s Law Graph.
Column 4: [Cr3“‘]t = [Cr3+]0 — [Cr(EDTA)‘]t
where, [Cr(EDTA)‘]t is Column 3 and
[Cr3+]0 is the original Cr3+ conc. at time 0 (a constant for each solution) Column 5: 1n [Cr3+][ Just take the natural log of each cell in Column 4. Column 6: l/[Cr3+][ Just take the reciprocal of Column 4. Some spreadsheets (Excel 7.0) can now do linear regression. You just tell it whcih columns you want to plot. I
wouldn’t suggest spending hours trying to ﬁgure out how unless you want to learn so you can use it in the future.
Just have it plot the points and draw your lines by hand if you can’t ﬁgure out how to do the linear regression or
the program won’t do it. What ever you do don't just tell it to connect the points so you get a jagged line. ...
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 Summer '07
 Zellmer
 Chemistry

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