Chemistry Intelligent Design

Surprisingly, we don’t know much about fire

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We are fond of ridiculing our ancestors for belief in phlogiston but a more accurate description of combustion, we are told, involves many uncertainties.

‘If you spoke to someone in the street and said “What do you need for fire?” They’d say you need air, you need a fuel, you need combustion. That’s it. It’s not wrong, but it gives a false impression of simplicity. Combustion is the prototypical complex system,’ [Ludovico] Cademartiri says. ‘The simplest hydrocarbon combustion – methane and oxygen – produces hundreds of different intermediates and byproducts through hundreds of different chemical reactions occurring at different rates. Those rates depend on temperature, which changes dramatically across a flame. Among the byproducts is soot, which is a solid with a sizeable heat capacity, so will get heated up and glow. For most people it’s hard to grasp how much complexity can hide beneath the reaction of just two reagents.’

This complexity is why fire remains so hard to grasp. While completing his postdoctoral work at Harvard University in the US, Cademartiri worked with fellow postdocs in George Whitesides’ lab and the US Defence Advanced Research Projects Agency to develop flame suppressants. At one point he asked one of the US Navy’s combustion experts when, on a chemical level, a fire is extinguished. ‘I asked if we can really determine the causal chain of events that lead to a specific flame going out. He said no.’

Kit Chapman, “The complexity of fire” at Chemistry World (July 20, 2020)

It may be worth keeping this in mind, what with the deadwood fires on the west coast of North America.

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