Oxygen + Photons: Uni- or Bi-Molecular Process?

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Discussion Overview

The discussion revolves around the classification of a chemical process involving oxygen and photons, specifically whether it should be considered a uni-molecular or bi-molecular process. The scope includes theoretical considerations regarding reaction mechanisms and the role of photons in chemical reactions.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions whether photons should be counted as a molecule in the context of defining the reaction order.
  • Another participant asserts that photons are not counted as molecules.
  • A later reply proposes that the process is bi-molecular because the reaction cannot occur without photons, treating photons as a reactant.
  • This participant provides a rate equation for the process, suggesting that under certain conditions, the reaction can appear to be pseudo-first or pseudo-zero-order due to the concentration of photons being constant.
  • A reference is provided for further reading on the topic, indicating that there are more detailed discussions and examples available.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether photons should be considered in the classification of the reaction order, leading to differing views on the nature of the process.

Contextual Notes

The discussion includes assumptions about the treatment of photons in chemical kinetics and the conditions under which the reaction order may change, which remain unresolved.

quietrain
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if i have oxygen + photons => products

if this is an elementary process, is this a uni-molecular process or a bi-molecular process?

i.e do we count photons as a molecule?

thanks!
 
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quietrain said:
do we count photons as a molecule?

We don't.
 
thanks!
 
quietrain said:
if i have oxygen + photons => products

if this is an elementary process, is this a uni-molecular process or a bi-molecular process?

i.e do we count photons as a molecule?

thanks!

It is bi-molecular because without photons there is not reaction

Photons are treated as any other reactant. The rate for your process is

V = k [ oxigen ] [ photons ]

Under certain conditions this second order looks as pseudo-first order or as pseudo-zero-order.

For example if photons are in excess then its concentration is approximately constant and the rate can be approximated by the pseudo-first-order

V = k' [ oxigen ]

with k' = k [ photons ]

See http://pubs.acs.org/doi/pdf/10.1021/ed082p37.3 and references therein for a more detailed discussion and examples.
 

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