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### Topic: How to Calculate Rate Constant?  (Read 89056 times)

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#### Leoonard

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##### How to Calculate Rate Constant?
« on: August 29, 2007, 08:01:23 AM »
Hi.

I have read alot of the other posts in this forum. And from what i can gather, i will have to plot a ln(rate) against a ln(concentration) graph. But how will that help me get a rate constant? What does the slope represent?

Just to confirm, i find the rate of the reaction by measuring the change in concentration over the time taken for it to take place is it? Rather, i can simply calculate how much mole is produced over a period of time is it?

Once again,the main question is how to get the rate constant of a reaction? Many Thanks!

#### Yggdrasil

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##### Re: How to Calculate Rate Constant?
« Reply #1 on: August 29, 2007, 02:08:38 PM »
It depends on the order of your reaction.  A first order reaction has a rate law:

rate = d[A]/dt = k[A]

Which has the integral form:

[A]t = [A]oe-kt

If you take the log of both sides of the equation:

ln([A]t) = ln([A]o) - kt

So, if you plot ln([A]t) v t, you get a line with y-intercept ln([A]o) and slope -k.

However, this method applies only for first order reactions.  For reactions that have different rate laws, you need to make different graphs.