Slope of 1st order RXNs


Moderators: Chem_Mod, Chem_Admin

Sophia Bozone 2G
Posts: 51
Joined: Fri Sep 29, 2017 7:07 am

Slope of 1st order RXNs

Postby Sophia Bozone 2G » Sun Mar 11, 2018 7:37 pm

Is the slope of 1st order reactions +k or -k, and what is time graphed against in terms of [A]?

Zane Mills 1E
Posts: 80
Joined: Fri Sep 25, 2015 3:00 am
Been upvoted: 1 time

Re: Slope of 1st order RXNs

Postby Zane Mills 1E » Sun Mar 11, 2018 7:51 pm

First order is -k slope with time vs ln[A]. Time vs just concentration [A] represents zero order (also -k slope).

Shawn Patel 1I
Posts: 54
Joined: Thu Jul 27, 2017 3:01 am

Re: Slope of 1st order RXNs

Postby Shawn Patel 1I » Sun Mar 11, 2018 8:49 pm

Hey,
The slope of both 0 and 1st order reactions is -k, second order reactions have a positive k slope. Time is graphed against ln(a).

Niyanta Joshi 1F
Posts: 30
Joined: Thu Jul 13, 2017 3:00 am

Re: Slope of 1st order RXNs

Postby Niyanta Joshi 1F » Sun Mar 11, 2018 9:04 pm

The integrated formula derived for the first order is [At] = [A0]*e^-kt. This gives an exponential graph of [At] against time and a decreasing graph with the slope of -k when graphed for ln[At] against time.

Michelle Lu 1F
Posts: 50
Joined: Thu Jul 27, 2017 3:01 am
Been upvoted: 1 time

Re: Slope of 1st order RXNs

Postby Michelle Lu 1F » Tue Mar 13, 2018 5:02 pm

If the graph of time plotted against ln[A] is linear, then this indicates that the reaction with respect to reactant A is 1st order. The integrated rate law for 1st order reactions is ln[A] = -kt + ln[Ao]. If you look at this equation as if it is in the form of y = mx + b, you can see that the slope would be -k, not +k, due to the negative sign in front of kt. For zero order reactions, the slope is also -k for graphs of time plotted against [A]. However, the slope for 1/[A] vs. time for 2nd order reactions is +k.

Wayland Leung
Posts: 51
Joined: Sat Jul 22, 2017 3:00 am
Been upvoted: 1 time

Re: Slope of 1st order RXNs

Postby Wayland Leung » Tue Mar 13, 2018 5:03 pm

The slope would be -k because the amount of reactants is decreasing over time.

Angel R Morales Dis1G
Posts: 50
Joined: Sat Jul 22, 2017 3:01 am

Re: Slope of 1st order RXNs

Postby Angel R Morales Dis1G » Thu Mar 15, 2018 8:03 pm

First order integrated rate law: ln[A]= -k*t+ln[A]
y= m*X + B

Zero Order Integrated Rate Law: [A]=−kt+[A]initial
Y= m*X+B

Sarah 2F
Posts: 33
Joined: Fri Sep 29, 2017 7:06 am

Re: Slope of 1st order RXNs

Postby Sarah 2F » Sat Mar 17, 2018 10:49 am

slope is -k

Nicole Jacobs 1C
Posts: 59
Joined: Thu Jul 13, 2017 3:00 am

Re: Slope of 1st order RXNs

Postby Nicole Jacobs 1C » Sat Mar 17, 2018 10:53 am

remember only the second order has a positive k slope

Cynthia Bui 2H
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

Re: Slope of 1st order RXNs

Postby Cynthia Bui 2H » Sat Mar 17, 2018 11:43 am

Slope is -K, a downward sloping graph.


Return to “First Order Reactions”

Who is online

Users browsing this forum: No registered users and 1 guest