Half life

$\frac{d[R]}{dt}=-k; [R]=-kt + [R]_{0}; t_{\frac{1}{2}}=\frac{[R]_{0}}{2k}$

Abigail Menchaca_1H
Posts: 104
Joined: Sat Sep 07, 2019 12:19 am

Half life

Where do you start when you determine the half life for a zero order reaction?

Posts: 103
Joined: Sat Aug 24, 2019 12:15 am

Re: Half life

to find the half life of the zero order reaction, you need to use the equation [A.5]=-kt+[A0], where A.5 is half the concentration of A0
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Serena Song 1A
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Re: Half life

You could also use t1/2 = [A]0/2k!

clairehathaway 2J
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Joined: Wed Sep 30, 2020 9:38 pm

Re: Half life

Today in lecture (3/3) Dr. Lavelle went through the derivation of finding the equation for the half-life of a zero-order reaction.
He started with the equation $[A] = -kt + [A]_{0}$, then when looking for $t = t_{1/2}$ we know that $[A] = 1/2[A]_{0}$. Then we can find that
$1/2[A]_{0} = kt_{1/2} + [A]_{0}$ which simplifies to $1/2[A]_{0} = kt_{1/2}$ and ultimately gives us the zero-order half life equation which is: $t_{1/2} = [A]_{0}/2*k$

DMaya_2G
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Re: Half life

You just simply use the equation t1/2 = [A]0/2k

apurva-3E
Posts: 142
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Re: Half life

We can use the reaction: t(1/2) = [A]0/2k

Xinying Wang_3C
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Joined: Wed Sep 30, 2020 9:39 pm

Re: Half life

you could plug numbers into the equation, t(1/2) = [A]0/2k

Samantha Lee 1A
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Re: Half life

The half life of a zero order reaction is $t_{1/2} = [A]_{o} / 2k$

The derivation of this equation was in 3/3 lecture. The integrated rate law for the zero order is $[A]_{t} = kt + [A]_{0}$. At $t = t_{1/2}$, [A] = 1/2*([A]_0). When we substitute 1/2[A]_0 into the equation for [A], the equation can be rearranged. The initial concentrations of A can be combined and then we solve for $t = t_{1/2}$. When we solve for $t = t_{1/2}$, we get the half life equation for the zero order.

We can either derive the equation every time you want to use the half life equation for each order, using its specific integrated rate law, or you can use the answer of the derivation. The half life equation will be the same for every problem that is of that order.

Stephen Min 1I
Posts: 95
Joined: Wed Sep 30, 2020 10:01 pm

Re: Half life

A 0 order reaction has a half life of t = [A]/2k, which depends on [A] initial.