Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Leoonard 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!
-
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.