A REACTION UNDECIDED

Some chemical reactions don’t go straight from reactants to products: They oscillate back and forth for a time before reaching a conclusion. One of these—the Belousov-Zhabotinsky reaction—is shown here at high speed (eight times faster than reality). The circular regions of the solution in this petri dish tip back and forth between being rich in bromate ions or in bromide ions. Although the reaction’s inner workings aren’t perfectly understood, the color changes arise from an indicator called ferroin, which turns blue when oxidized and red when reduced by bromine ions in their different oxidation states. After about 30 minutes, this reaction eventually dies down, the solution settling into a dull, blue color.

Credit: Stephen Morris/YouTube

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