Register to reply

3 Questions regarding reaction kinetics- please help me out.

by christian0710
Tags: kinetics, reaction
Share this thread:
christian0710
#1
Jul10-14, 08:31 AM
P: 209
Hi I need some help understanding reaction kinetics, and I’m trying to get an overview, so I’d really appreciate some help. I have 3 individual/quite unrelated questions, if you have time to answer one that would be very much appreciated.

1. In what situations dos the Definition of the reaction rate for a general reaction Hold true?

aA + Bb --> pP+qQ

-(1/a)*(d[A]/dt)= -(1/b)*(d[B]/dt) = -(1/p)*(d[P]/dt) = -(1/q)*(d[Q]/dt)

I would assume this definition only holds true when all the rates are equal, so this does not apply for reactions where the rate of A is different from the rate of B (if this is possible)

2. If the rate of A is slower than the Rate of B, would they then not be comsumed at the same RATE because A would be the limiting factor, the equation -(1/a)*(d[A]/dt)= -(1/b)*(d[B]/dt) holds true for all reactions?

3. Is it true that if the rate law for A + B --> C +D is givn by -d[A]/dt = k[A]^n[B]^m with respect to A, then it might be different with repsect to B? So -d[B]/dt might be different (slower or faster) than -d[A]/dt, so the -d[A]/dt=-d[B]/dt = k[A]^n*[B]^m only holds true for elementary reactions, while for complex reactions the rate law for -d[A]/dt could be equal to k[A][B] raised to a first order while -d[B]/dt could be equalt to k[A]^2[B]^1 (something different?)
Phys.Org News Partner Chemistry news on Phys.org
Four billion-year-old chemistry in cells today
A new approach to creating organic zeolites
Spinach could lead to alternative energy more powerful than Popeye
Borek
#2
Jul10-14, 08:46 AM
Admin
Borek's Avatar
P: 23,363
Quote Quote by christian0710 View Post
I would assume this definition only holds true when all the rates are equal, so this does not apply for reactions where the rate of A is different from the rate of B (if this is possible)
It is not possible. I already told you somewhere else that we use stoichiometric coefficients to make sure rates of the reaction for all substances involved are identical.
christian0710
#3
Jul10-14, 08:55 AM
P: 209
Hi borek, yes i was a bit confused on what question you were answering but now it seems more clear to me: What you are saying is that No matte what reaction we have (Zero order, first order, second order, complex) the equation -(1/a)*(d[A]/dt)= -(1/b)*(d[B]/dt) = -(1/p)*(d[P]/dt) = -(1/q)*(d[Q]/dt) is true? and in some cases the rate of any of the reactants might display the following relationship = k[A]^m[B]^n (for complex reactions) and in elementary reactions the orders of the reaction equals the koefficients of the reactants?

If this is a correct understanding, I'm really happy :)

christian0710
#4
Jul10-14, 08:58 AM
P: 209
3 Questions regarding reaction kinetics- please help me out.

Ohh yes an just to make sure it's 100% clear for me:

If -(1/a)*d[A]/dt)=k[A]^m[B]^n

Then This must also be true

-(1/b)*(d[B]/dt)=k[A]^m[B]^n

:)
Borek
#5
Jul10-14, 11:30 AM
Admin
Borek's Avatar
P: 23,363
Quote Quote by christian0710 View Post
No matte what reaction we have (Zero order, first order, second order, complex) the equation -(1/a)*(d[A]/dt)= -(1/b)*(d[B]/dt) = -(1/p)*(d[P]/dt) = -(1/q)*(d[Q]/dt) is true?
and in some cases the rate of any of the reactants might display the following relationship = k[A]^m[B]^n (for complex reactions) and in elementary reactions the orders of the reaction equals the koefficients of the reactants?
Quote Quote by christian0710 View Post
If -(1/a)*d[A]/dt)=k[A]^m[B]^n

Then This must also be true

-(1/b)*(d[B]/dt)=k[A]^m[B]^n
Yes, yes, yes & yes.
christian0710
#6
Jul10-14, 11:50 AM
P: 209
Thank you very much Borek - Now I'm really happy :D


Register to reply

Related Discussions
Reaction Kinetics Question Biology, Chemistry & Other Homework 0
Enzyme Reaction Kinetics Please Help Biology, Chemistry & Other Homework 1
Kinetics/reaction rate Biology, Chemistry & Other Homework 1
Reaction kinetics question Introductory Physics Homework 1
Reaction kinetics Chemistry 1