Bray-Liebhafsky reaction
Encyclopedia
The Bray–Liebhafsky reaction is a chemical clock
first described by William C. Bray in 1921 and the first oscillating reaction in a stirred homogeneous solution. He investigated the role of the iodate
(IO3-), the anion of iodic acid
in the catalytic conversion of hydrogen peroxide
to oxygen
and water
by the iodate. He noticed that the concentration of iodine molecules oscillated and that oxygen did build up pulsating.
An increase in temperature reduces the cycle in the range of hours. This oscillating reaction consisting of free radical on non-radical steps was investigated further by his student Herman A. Liebhafsky, hence the name Bray–Liebhafsky reaction. During this period, most chemists rejected the phenomenon and tried to explain the oscillation by invoking heterogeneous impurities.
A fundamental property of this system is that hydrogen peroxide has a redox potential which enables the simultaneous oxidation of iodine
to iodate
:
and the reduction
of iodate back to iodine:
Between these two reactions the system oscillates causing a concentration jump of the iodide and the oxygen production. The net reaction is:
necessitating a catalyst and IO3-.
Chemical clock
A chemical clock is a complex mixture of reacting chemical compounds in which the concentration of one or more components exhibits periodic changes....
first described by William C. Bray in 1921 and the first oscillating reaction in a stirred homogeneous solution. He investigated the role of the iodate
Iodate
An iodate is a conjugate base of iodic acid. In the iodate anion, iodine is bonded to three oxygen atoms and the molecular formula is IO3−. The molecular geometry of iodate is trigonal pyramidal....
(IO3-), the anion of iodic acid
Iodic acid
Iodic acid, HIO3, can be obtained as a white solid. It dissolves in water very well, but it also exists in the pure state, as opposed to chloric acid or bromic acid. Iodic acid contains iodine in the oxidation state +5 and it is one of the most stable oxo-acids of the halogens in its pure state....
in the catalytic conversion of hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
to oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
by the iodate. He noticed that the concentration of iodine molecules oscillated and that oxygen did build up pulsating.
An increase in temperature reduces the cycle in the range of hours. This oscillating reaction consisting of free radical on non-radical steps was investigated further by his student Herman A. Liebhafsky, hence the name Bray–Liebhafsky reaction. During this period, most chemists rejected the phenomenon and tried to explain the oscillation by invoking heterogeneous impurities.
A fundamental property of this system is that hydrogen peroxide has a redox potential which enables the simultaneous oxidation of iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
to iodate
Iodate
An iodate is a conjugate base of iodic acid. In the iodate anion, iodine is bonded to three oxygen atoms and the molecular formula is IO3−. The molecular geometry of iodate is trigonal pyramidal....
:
- 5 H2O2 + I2 → 2 IO3- + 2 H+ + 4 H2O
and the reduction
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
of iodate back to iodine:
- 5 H2O2 + 2 IO3- + 2 H+ → I2 + 5 O2 + 6 H2O
Between these two reactions the system oscillates causing a concentration jump of the iodide and the oxygen production. The net reaction is:
- 2 H2O2 → 2 H2O + O2
necessitating a catalyst and IO3-.