Half Life Equations


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504594108
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Joined: Fri Sep 25, 2015 3:00 am

Half Life Equations

Postby 504594108 » Tue Feb 16, 2016 8:45 pm

How do you know when to use ln .5=-kt or ln [A]= -kt + [A]initial ?

Cat Larcheveque 2E
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

Re: Half Life Equations

Postby Cat Larcheveque 2E » Tue Feb 16, 2016 8:57 pm

I think the first equation would be used when calculating the half life for a reaction.

Kaitlin Ross 3E
Posts: 25
Joined: Fri Sep 25, 2015 3:00 am

Re: Half Life Equations

Postby Kaitlin Ross 3E » Mon Feb 22, 2016 12:13 pm

When calculating half-life, [A]=1/2[A]original so when you use the equation ln[A]= -kt + ln[A]original you can plug in .5[A]original for [A] to get ln(.5[A]original)= -kt + ln([A]original) which equals ln(.5[A]original/[A]original)=-kt. The [A]original cancels out leaving you with ln(.5)=-kt


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