Bray–Liebhafsky reaction
Chemical clock involving hydrogen peroxide and iodine
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Through Oxygen, Water and Radical (chemistry)
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:
- 5 H2O2 + I2 → 2 IO−
3 + 2 H+ + 4 H2O
and the reduction of iodate back to iodine:
- 5 H2O2 + 2 IO−
3 + 2 H+ → I2 + 5 O2 + 6 H2O
Between these two reactions the system oscillates causing a concentration jump of the iodate and iodine and thus differing oxygen production. The net reaction is:
- 2 H2O2 → 2 H2O + O2
necessitating a catalyst and IO−
3.