Everyday entropy: chemistry


Chemistry is the one field where entropy is accepted and understood.   Much like plants and bull riders, chemists don’t want their substances to go anywhere in particular or do anything other than react and transform entropically.  Entropy is what makes things happen in chemistry, and whether it increases or decreases is immaterial.  This is why Arieh ben Naim can argue rationally and correctly that physical entropy is a measure of information – he isn’t interested in energy as force and function.  For a mechanical engineer, entropy means something completely different – entropy is the thing that stops things from doing what they’re supposed to do.

Another reason for ben Naim’s total comfort with entropy is that chemistry is essentially the study of relationships between atoms in a molecule and molecules in a mass.  In the field of chemistry, entropy is clearly and measurably related to the energy that goes into making or destroying those relationships. Sure, those reactions may create pressure or heat that may be used to drive machines, but that driving business is not chemistry, it’s mechanics, and chemists don’t care whether the energy in their substances goes one way or another.  At the scale of atomic and molecular relationships, entropy doesn’t look like lost work or disorder.  Brownian motion dances and blackbody radiation shines irrepressibly at the level of chemical compounds, so chemists feel nothing like the sense of betrayal or subversion that machinists and labourers feel when confronted with the constraints of entropy.

Climate change is one of the few observable intrusions of chemical relationships into the macroscopic world, so it is not surprising that populists have portrayed it as a subversive betrayal of nationalist values.  But even for physical scientists, the chemical entropy of carbon dioxide in the atmosphere derived from the oxidation and hydrolysis of hydrocarbons is startling because, thermodynamically, space seems like an infinite heat sink.  But, because heat has to get through the atmosphere entropically, the relationships between atoms and molecules passing that energy up into space matters.  The thermal contribution of fossil fuel combustion may be trivial, but its chemical contribution is invisibly spectacular.


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