half-life


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Emma Li 2C
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Joined: Fri Sep 29, 2017 7:07 am
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half-life

Postby Emma Li 2C » Sun Mar 04, 2018 9:40 pm

Why is the half-life of reactant in a first order reaction independent of initial concentration?

Thank you!

Harsha 1J
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

Re: half-life

Postby Harsha 1J » Sun Mar 04, 2018 9:49 pm

This is because the half-life of a first order reaction is a constant.

Nishma Chakraborty 1J
Posts: 51
Joined: Fri Sep 29, 2017 7:04 am

Re: half-life

Postby Nishma Chakraborty 1J » Sun Mar 04, 2018 9:50 pm

I think it's because of its derivation from the original formula: ln[A]=-kt +ln[Ainitial].

When [A]=1/2[Ainitial],

ln(1/2[Ainitial])= -kt +ln [Ainitial]
ln(1/2[Ainitial])-ln[Ainitial]= -kt
ln{(1/2[Ainitial])/[Ainitial]= -kt

Through this, the initial concentration of A cancels out, and t=(ln2)/k.

Hope this helps!


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