K constant


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MorganYun1H
Posts: 59
Joined: Thu Jul 13, 2017 3:00 am

K constant

Postby MorganYun1H » Sun Mar 04, 2018 6:11 pm

can someone explain what Lavelle means when he says that a negative k means negative slope, but it is negative because we want a positive k? How do you get a positive k from a negative k?

Julianna Thrasher 1B
Posts: 27
Joined: Thu Jul 27, 2017 3:00 am

Re: K constant

Postby Julianna Thrasher 1B » Sun Mar 04, 2018 6:53 pm

For a first order reaction, the integrated rate law is: ln[A] = -kt + ln[A]0. If you set ln[A]=y and -k=m you can get a typical slope equation in the form of y=mx+c. Since -k=m then the slope of the curve is negative so a negative k implies a negative slope. A 1st order reaction of ln[A] vs time means the graph will have a slope of -k.
The only way there is a positive k for a first order reaction is for the first order half life equations, Rate = k[A0]e^-kt.
Professor Lavelle discussed this in Lecture 19 on 2/26/18.

Lindsay Kester 2L
Posts: 29
Joined: Thu Jul 27, 2017 3:00 am

Re: K constant

Postby Lindsay Kester 2L » Sun Mar 04, 2018 8:43 pm

When we graph K, we make it negative, because the reaction is using up reactants (at least initially). K itself is usually positive.

MorganYun1H
Posts: 59
Joined: Thu Jul 13, 2017 3:00 am

Re: K constant

Postby MorganYun1H » Mon Mar 05, 2018 9:43 am

So then will we ever see a positive k value?


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