21.10.2014 Views

Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

9.1 Chain reactions and chain explosions 204<br />

(2) Solution with steady state assumption for [X] at À (i.e, after the induction<br />

time ):<br />

[X]<br />

≈ 0 (9.7)<br />

<br />

y<br />

[X] <br />

= 1<br />

[A] (9.8)<br />

4<br />

y Considering the free radical concentration profile [X ()], no desasters are happening.<br />

I<br />

Figure 9.1: Evolution of the free radical concentration in a normal chain reaction.<br />

9.1.2 Chain reactions with branching<br />

I<br />

Reaction scheme:<br />

(1) A → X chain initiation<br />

(3) X+B→ P+ X chain branching<br />

= branching factor<br />

(4) X → A chain termination<br />

I<br />

Most important example for a chain branching reaction:<br />

H+O 2 → OH + O (9.9)<br />

This reaction is responsible for flame propagation in all hydrocarbon flames: Since H is<br />

small, it has the highest diffusion coefficient and diffuses rapidly into the unburnt gases.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!