## determining Kr

$\frac{d[R]}{dt}=-k[R]; \ln [R]=-kt + \ln [R]_{0}; t_{\frac{1}{2}}=\frac{0.693}{k}$

Mallika Singh 1G
Posts: 99
Joined: Sat Aug 24, 2019 12:16 am

### determining Kr

When given a graph full of points of ln[A] vs t, all we need to do to find Kr is determine the slope? Do we use the typical slope equation (change in rise/run)?

Caitlyn Tran 2E
Posts: 100
Joined: Fri Aug 09, 2019 12:15 am

### Re: determining Kr

Yes, you can find k by calculating the slope. Since it is linear, you can use rise over run. If you look at the examples in the textbook, they use two points on the line to calculate the slope. Hope this helps!

JasonLiu_2J
Posts: 109
Joined: Sat Aug 24, 2019 12:17 am

### Re: determining Kr

Also to add on, remember that for a first order reaction, the slope of the graph ln[A] vs time is -k, so you would need to multiply it by negative 1 to find the value of the rate constant.

Emily Burghart 1k
Posts: 50
Joined: Wed Sep 18, 2019 12:17 am

### Re: determining Kr

JasonLiu_2J wrote:Also to add on, remember that for a first order reaction, the slope of the graph ln[A] vs time is -k, so you would need to multiply it by negative 1 to find the value of the rate constant.

Why are we able to just multiply the slope by -1 to find the rate constant?

Kyle Rex 1K
Posts: 50
Joined: Sat Aug 17, 2019 12:16 am

### Re: determining Kr

because for a first order rxn, the plot for a linear slope would be: ln[A]= -kt + ln[A(initial)]

When comparing it to the linear form y=mx+b, you'll see that -k is m, or the slope. so to find k, you would multiply the slope, -k, by -1

Sofia Barker 2C
Posts: 101
Joined: Wed Sep 18, 2019 12:21 am

### Re: determining Kr

Yes, you would find the value of -k, the slope, through rise over run. The absolute value of the slope is equal to k.