15.31 6th Edition


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Janice Park 1E
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Joined: Fri Sep 28, 2018 12:22 am

15.31 6th Edition

Postby Janice Park 1E » Mon Mar 11, 2019 8:08 pm

For question 31 in Chapter 15 of the 6th Edition of the textbook, we are looking for the half life of iodine-131.
I know that we use the equation t(halflife) = 1/(k*initial concentration), but the answer key shows that t(halflife) is (1/k) * ln2.
Where does the ln2 come from? Is that supposed to be related to the initial concentration?

Sam Joslyn 1G
Posts: 34
Joined: Fri Sep 28, 2018 12:20 am

Re: 15.31 6th Edition

Postby Sam Joslyn 1G » Mon Mar 11, 2019 8:39 pm

ln2/k=t1/2 for first-order reactions, so I'm guessing the the decay of iodine-131 is a first-order reaction. It would follow that you use this equation, not the half-life equation for second-order reactions which is indeed t1/2=1/k[A]0

Alexa Tabakian 1A
Posts: 38
Joined: Fri Sep 28, 2018 12:20 am

Re: 15.31 6th Edition

Postby Alexa Tabakian 1A » Mon Mar 11, 2019 8:56 pm

Make sure the order of the reaction corresponds to the right half-life equation.

harshitasarambale4I
Posts: 58
Joined: Fri Sep 28, 2018 12:26 am

Re: 15.31 6th Edition

Postby harshitasarambale4I » Mon Mar 11, 2019 9:29 pm

15.31 is not on the syllabus.


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