# Chemical Kinetics Query

1. Feb 21, 2005

### maverick280857

HI

While working on some chemical kinetics problems, I came across the statement, the fraction of activated molecules is $10^{-15}$ in a problem where some other constants were also provided and the half life was to be found (for a first order reaction). My specific query is:

Is this fraction equal to the probability factor in the Arrhenius Equation? That is, is this equal to P where

$$k = APe^{-E_{act}/RT}$$

where k = rate constant, A = frequency factor, P = probability factor, $E_{act}$ = activation energy and T = absolute temperature?

Or is it something else?

Thanks and cheers
vivek

Last edited: Feb 21, 2005
2. Feb 21, 2005

### GCT

It'll be better for you if you were to post the exact problem instead of having us guess around (not to sound rude).

3. Feb 21, 2005

### Gokul43201

Staff Emeritus
The fraction of activated molecules is actually the exponential term.

A and P are related to collision rates (T dependent) and molecular geometries (steric effects).

4. Mar 1, 2005

### maverick280857

Thanks Gokul, you were right about the exponential term.

Cheers
vivek