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Half Life and k

Posted: Sat Mar 09, 2019 10:50 am
by Simmi Diwanji 2B
Why is there always an inverse relationship between half life and the rate constant k?

Re: Half Life and k

Posted: Sat Mar 09, 2019 11:34 am
by Christina Chang 1C
I think this is because the half-life equation is derived from the rate law and therefore if you solve for t1/2, k becomes inversely proportional to t1/2.

Re: Half Life and k

Posted: Sat Mar 09, 2019 12:36 pm
by Ava Kjos 1D
the equation of half life is always t(1/2)=ln2/kr.

The proof for this is given in 7B.2 in the 7th edition textbook.

Re: Half Life and k

Posted: Sat Mar 09, 2019 3:25 pm
by Michael Novelo 4G
because half life will always taking the form of k1/2 = 1/k[A]o (for a zero order reaction) since k is always on the bottom/denominator for any order if it increases then the value of k1/2 (half life) decreases and vice versa

Re: Half Life and k

Posted: Sat Mar 09, 2019 6:39 pm
by MadelineHlobik
How exactly do we calculate half life?

Re: Half Life and k

Posted: Sat Mar 09, 2019 7:08 pm
by ran2000
This is because k is associated with how fast a reaction runs. If the reaction runs faster then the amount of time needed for the substance to fall to half its original decreases. Hence, K is inversely proportional to Half life.

Re: Half Life and k

Posted: Sat Mar 09, 2019 10:25 pm
by amogha_koka3I
Will we be required to know how to derive half-life equations for each order of reaction

Re: Half Life and k

Posted: Sun Mar 10, 2019 8:46 pm
by BenJohnson1H
Would it be correct that you need to know either the t1/2 or the [R]o to solve anything in the half life equation?

Re: Half Life and k

Posted: Sun Mar 10, 2019 10:17 pm
by Brayan Claros
half life turns into k1/2 = 1/k[A]o for a zero order reaction since k is usually a denominator for an order. then if the order increases then the value of k1/2 half life decreases. its the same the other way around

Re: Half Life and k

Posted: Sun Mar 10, 2019 10:41 pm
by madisondesilva1c
amogha_koka3I wrote:Will we be required to know how to derive half-life equations for each order of reaction


I believe this is on the syllabus, and was gone over in lecture so I feel that we are responsible for knowing how to do this.

Re: Half Life and k

Posted: Sat Mar 16, 2019 1:32 am
by madisondesilva1c
Half life and k are related differently upon what order the reaction proceeds in. The most common half life problems use first order reactions and this is simply .693/k=t1/2. Therefore you can see the inverse relationship that exists.

Re: Half Life and k

Posted: Sat Mar 16, 2019 7:21 pm
by He whose name cannot be spoken
Half life is defined as "the time it takes for the concentration of reactant to be half of the original", while k is "the rate at which the reactant is becoming product". The higher k is, the faster the reactant becomes product, the lower the half life will be.