Half Lives? [ENDORSED]

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

Hellen Truong 2J
Posts: 50
Joined: Sat Jul 22, 2017 3:00 am
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Half Lives?

Is it accurate to use half lives for questions that say something like 1/4 of the reactant is remaining?

Christine Wastila 1H
Posts: 61
Joined: Fri Sep 29, 2017 7:04 am

Re: Half Lives?

Yes because that would indicate that the species has undergone two half-lives.

skalvakota2H
Posts: 52
Joined: Sat Jul 22, 2017 3:01 am

Re: Half Lives?

In general, at any stage of the reaction, we can find how much of a reactant is remaining after n half-lives by (1/2)^n [A]0. Thus, if 1/2 is a factor of the remaining amount, then it is allowed to use the half life method.

CalebBurns3L
Posts: 47
Joined: Fri Sep 29, 2017 7:07 am

Re: Half Lives?

Yes, you would simply calculate the half life and then multiple it by 2 get the time to reach 1/4 of the reactant remaining.

Ilan Shavolian 1K
Posts: 58
Joined: Fri Sep 29, 2017 7:03 am

Re: Half Lives?

yes because 1/4th product is = the amount left after two half lives

Fatima_Iqbal_2E
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Re: Half Lives?  [ENDORSED]

Yes, because you would be able to multiply the half-life by the number of times it occurred to find the time it would take to reach the new concentration.

snehabhargava
Posts: 52
Joined: Thu Jul 13, 2017 3:00 am

Re: Half Lives?

yes, because 1/4 is the half life of the half life.

Timothy Kim 1B
Posts: 62
Joined: Fri Sep 29, 2017 7:04 am

Re: Half Lives?

Yes, half-life works for that fraction.