Units of Reactions. [ENDORSED]
Moderators: Chem_Mod, Chem_Admin
-
- Posts: 10
- Joined: Fri Sep 25, 2015 3:00 am
Units of Reactions.
Can someone please explain to me how to know which unit of k to use for zero order, first order, and second order reactions? Why are they different for each order?
-
- Posts: 25
- Joined: Fri Sep 25, 2015 3:00 am
Re: Units of Reactions.
Units of k for a zero order reaction is just M*s^-1 because the Rate = k. There is no concentration that affects the equation.
Units of k for a first order reaction is s^-1 because Rate = k[A]. Since there is one concentration value, s^-1 must multiply with M to give us a rate of M*s^-1.
Finally, units of k for a second order reaction is M^-1 * s^-1 because Rate = k[A]2. It makes sense that M^-1 must cancel out M^2 to give us a rate of M*s^-1.
Units of k for a first order reaction is s^-1 because Rate = k[A]. Since there is one concentration value, s^-1 must multiply with M to give us a rate of M*s^-1.
Finally, units of k for a second order reaction is M^-1 * s^-1 because Rate = k[A]2. It makes sense that M^-1 must cancel out M^2 to give us a rate of M*s^-1.
-
- Posts: 51
- Joined: Fri Sep 29, 2017 7:05 am
-
- Posts: 57
- Joined: Thu Jul 27, 2017 3:01 am
Re: Units of Reactions.
If you forget the units, plug in mol/Ls for the rate and mol/L for the concentration of A and find k according to what power A is raised to (so that the units cancel on both sides of the equation). I usually don't memorize the units for the rate constant but find it like this when I need to.
-
- Posts: 53
- Joined: Fri Sep 29, 2017 7:03 am
Re: Units of Reactions.
What helps most is just knowing that rate must be defined as mol/L*S so whatever reactants you have and what they multiply out to, just convert K to make sure the final units are in mol/L*S
-
- Posts: 58
- Joined: Fri Sep 29, 2017 7:03 am
Re: Units of Reactions. [ENDORSED]
Just subtract 1 from the total order of the reactants (x), and than put Lx / molx * s
Return to “First Order Reactions”
Who is online
Users browsing this forum: No registered users and 7 guests