Thread: Rate Laws
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Nov21-09, 03:56 PM
P: 52
The first-order decomposition of a colored chemical species, X, into colorless products is monitored with a spectrophotometer by measuring changes in absorbance over time. Species X has a molar absorptivity constant of 5.00 x 10^3 cm^ -1 M^ -1 and the path length of the cuvette containing the reaction micture is 1.00 cm. The data from the experiment are given in the table below.
[X] Absorbance Time(min)

? 0.600 0.0
4.00 x 10^ -5 0.200 35.0
3.00 x 10^ -5 0.150 44.2
1.5 x 10^ -5 0.075 ?

a) calculate the initial concentration of the colored species.
- I got 1.2 * 10 ^ -4 is that right?

b) calculate the rate constant for the first-order reaction using the values given for concentration and time. Include unites with your answer.
- I got 0.0314, however I do not know if this is correct and will the units be cm ^ -1 M ^ -1

c) calulate the number of minutes it takes for the absorbace to drop from 0.600 to 0.075
how do you do this?
d) calculate half-life of the reation. Include units with your answer.
question # 3

I WOULD REALLY APPRECIATE if you help me out, it is really confusing!

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