## Half-life of first order reactions [ENDORSED]

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

Kate Zeile 2D
Posts: 39
Joined: Sat Jul 22, 2017 3:01 am

### Half-life of first order reactions

I understand from the half-life equation that the half-life of a first order reaction does not depend on concentration and that, therefore, it has the same value at all stages of the reaction. However, this does not make sense to me. How can the half-life be the same at all stages of the reaction, even if the concentration changes?

Alexander Peter 1F
Posts: 20
Joined: Wed Jun 28, 2017 3:00 am

### Re: Half-life of first order reactions

To my understanding, half-life doesn't change because the rate it's getting rid of a substance is proportional to the amount. So, if there's more of a substance then it'll dissipate at a faster rate. Zero-order reaction, on the other hand, I think eliminates a given amount of a substance at intervals, which is why it's half-life would change if you change the amount of substance there is.

Hopefully, I'm not getting this all wrong. X)

April P 1C
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Joined: Thu Jan 12, 2017 3:01 am

### Re: Half-life of first order reactions

The half-life of a substance is the time needed for its concentration to fall one-half its initial value. It doesn't depend on concentration.

Xin He 2L
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Joined: Fri Sep 29, 2017 7:05 am

### Re: Half-life of first order reactions

The half life of any substance would be the time required for the substance to decay to half it's original value.

Guangyu Li 2J
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### Re: Half-life of first order reactions  [ENDORSED]

Half-life represents the time that a material is decayed to half of its original content. This variable is actually independent of the concentrations. More specifically, the time a given material decays from its original content to half of it is the same as that used to decay from half of it to a quarter of it.