Briggs-Rauscher Mechanism: The Chemical Color Clock
Briggs-Rauscher Mechanism: The Chemical Color Clock
The reactions involved in the Briggs–Rauscher (BR) mechanism are the following:
2++⇀HOI+
+
H
-
I
-
IO
3
HIO
2
+
H
-
I
HIO
2
HOI++⇌+O
+
H
-
I
I
2
H
2
-
IO
3
HIO
2
+
H
IO
2
H
2
2⇀HOI++
HIO
2
-
IO
3
+
H
IO
2
H
2
2+
Mn
HIO
2
2+
MnOH
2+
MnOH
H
2
O
2
HO
2
2+
Mn
H
2
2⇀+
HO
2
H
2
O
2
O
2
I
2
+
H
-
I
HOI+⇀+++O
H
2
O
2
O
2
+
H
-
I
H
2
where is malonic acid.
MA
Suppose these reactions take place in an open reactor. Then, under certain circumstances, the color of the solution in the reactor shows regular oscillation between amber and dark blue.
This Demonstration simulates the BR mechanism in a flow reactor and shows that the rate expressions given in [1] predict the observed topology of the "cross-shaped phase diagram" in which both bistability and oscillations appear as the initial condition (i.e. initial condition 1 or 2) and the input flows of the reactant species and (i.e. and ) are varied.
1
3
X
10
X
30
The Demonstration shows the presence of a limit cycle for specific values of and (e.g. =0.035 and =) and sustained oscillations for the compositions. Time series for the compositions of , , , and (i.e. (t), (t), (t), and (t), respectively) are shown in green, brown, magenta, and blue, respectively. For other values of and (e.g. =0.04 and =2.4), one can see bistability. Indeed, two steady states are observed depending the choice of the initial condition (i.e. initial condition 1 or 2). Initial condition and steady state are shown by the blue and green dots, respectively.
X
10
X
30
X
10
X
30
-6
10
-
IO
3
-
I
I
2
HIO
2
x
2
x
3
x
4
x
5
X
10
X
30
X
10
X
30
-6
10