Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...
Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ... Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...
3.6 Oscillating reactions* 71 Here, A and B are reactants, R and S are final products, and X and Y are intermediates. The autocatalytic reaction is reaction (3). Rate equations (using “dimensionless time” = 4 ) and steady-state concentrations: [X] [X] Steady-state concentrations: = · [X] = 1 [A] − 2 [B] [X] + 3 [X] 2 [Y] − 4 [X] 4 (3.201) = · [Y] = 2 [B] [X] − 3 [X] 2 [Y] 4 (3.202) [X] [Y] = 1 [A] 4 (3.203) = 2 4 [B] 1 3 [A] (3.204) We now investigate the effect of small displacements from steady-state by [X] and [Y]. The reaction rates respond to these displacements according to ⎛ ⎞ ⎛ ⎞ ⎝ [X] · ⎠ [X] and ⎝ [Y] · ⎠ [Y] (3.205) [X] [Y] y • The steady-state is stable if ⎛ ⎞ ⎝ [X] · ⎠ [X] • The steady-state is unstable if ⎛ ⎞ ⎝ [X] · ⎠ [X] • Stability criterion: ⎛ ⎞ ⎝ [X] · ⎠ [X] ⎛ ⎞ + ⎝ [Y] · ⎠ [Y] ⎛ ⎞ + ⎝ [Y] · ⎠ [Y] ⎛ ⎞ + ⎝ [Y] · ⎠ [Y] 0 (3.206) ≥ 0 (3.207) = 2 [] − 2 1 3 [] 2 − 1 (3.208) 4 4 2 c) Belousov-Zhabotinsky reaction Oxidation of malonic acid to CO 2 by bromate, catalyzed by cerium ions in acidic solution: 2BrO − 3 +3CH 2 (COOH) 2 +2H + −→ 2BrCH(COOH) 2 +3CO 2 +4H 2 O (3.209) The reaction is probed by addition of the redox indicator ferroin/ferriin: The color varies between red and blue depending on the concentrations of Ce 4+ and Ce 3+
3.6 Oscillating reactions* 72 I Figure 3.7: Mechanism of the Belousov-Zhabotinsky reaction. I Figure 3.8: Phases I - III of the Belousov-Zhabotinsky reaction.
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3.6 Oscillating reactions* 72<br />
I<br />
Figure 3.7: Mechanism of the Belousov-Zhabotinsky reaction.<br />
I<br />
Figure 3.8: Phases I - III of the Belousov-Zhabotinsky reaction.
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