Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Rate of Reaction Mg and HCl
Name: Trang
Status: student
Grade: Key Stage 4
Location: Great Britain
Date: August 2008


Question:
Hi, I am currently working on a case study about rate of reaction. I did an experiment with Mg and HCl. according to the collisions theory, every time I double the concentration of HCl, the rate of reaction will double as it is inversely proportional to each other however when I calculated my proportion I found out that my rate of reaction is actually in proportion of 1 to 4. I am not able to explain why. Can you please help me?



Replies:
Trang,

The rate of a reaction (R) is a function of the rate constant (k), the concentration of reactant A ([A]) raised to some power (m) which is either 0, 1, or 2. If there is another reactant B ([B]) than this will also be included. Mathematically, this is written as:

R = k [A]^m [B]^n

Assuming that you hold [B] constant (do not change the concentration (or if B is a pure solid), and if we divide the equation 1 for a reaction with a concentration of A1:

R1 = k [A1]^m

by the equation describing another instance of this reaction using a different concentration A2:

R2 = k [A2]^m

then what we have is:

R1/R2 = ([A1]/[A2])^m

If we were smart enough to make sure that A1 is twice that of A2, then the above reaction reduces to:

R1/R2 = 2^m

Now you can see that if m = 0 then R1/R2 = 1, if m=1 then R1/R2 = 2, and if m=2 then R1/R2 = 4.

I think from this you can figure out the explanation for your observations.

Greg (Roberto Gregorius)



Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory