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Volume 89 Issue 47 | p. 35
Issue Date: November 21, 2011 | Web Date: December 12, 2011

Combustion

Bloggers pen essays celebrating their favorite chemical reactions
Department: Science & Technology
Keywords: blog carnival, chemical reactions, organic reactions
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SURPRISINGLY SIMPLE
Combustion sustains life and may one day end it.
Credit: Ashutosh Jogalekar
This simple reaction sustains life and may one day end it. Combustion reaction drawn by Ashutosh Jogalekar
 
SURPRISINGLY SIMPLE
Combustion sustains life and may one day end it.
Credit: Ashutosh Jogalekar
[+]Enlarge
Credit: Courtesy of Ashutosh Jogalekar
Ashutosh (Ash) Jogalekar head shot
 
Credit: Courtesy of Ashutosh Jogalekar

Ashutosh (Ash) Jogalekar is a chemist involved in building molecular models of chemical and biological systems. He is interested in the history, philosophy, and sociology of science and blogs at wavefunction.fieldofscience.com.

My favorite reaction is so elementary that it will occupy barely a tenth of the space on a napkin or T-shirt. And it’s a reaction so important that it both sustains life and has the potential to end it.

By now you might have guessed it. It’s the humble combination of hydrocarbons with oxygen, known to all of us as combustion.

Combustion is, in one line, a statement about our world that packs at least as much information into itself as all of humanity’s accumulated wisdom and follies.

While serving as the fundamental energy source for life and all the glory of evolution, combustion also drives wars, makes enemies out of friends, divides and builds ties between nations, and will without a doubt be responsible for the fate of human civilization.

Let’s look at the components of this ubiquitous process. First, the hydrocarbon itself. Humanity launched itself onto a momentous trajectory when it learned how to dig carbon out of the ground and use it as fuel. Since then we have been biding our time for better or worse. The laws of quantum mechanics could not have supplied us with a more appropriate substance. Carbon in stable hydrocarbons is in its most reduced state, which means that you can get a bigger bang out of your buck by oxidizing it compared with almost any other substance. What billions of controlled experiments over the years in oil and natural gas refineries and coal plants have proven is that you really can’t do better than carbon when it comes to balancing energy density against availability, cost, ease of handling, and transportation and safety.

The second component of the chemical equation is oxygen. Carbon can burn under a wide range of oxygen concentrations, which is a blessing because it means that we can safely burn it in a very controlled manner. Varying the amount of oxygen can also lead to different products and can minimize the amount of soot and toxic by-products. The marriage of carbon and oxygen is a wonderfully tolerant and productive one, and we have gained enormously from this union.

The right side of the combustion equation is where our troubles begin. First off, water. It may seem like a trivial, harmless by-product of the reaction, but it’s precisely its benign nature that allows us to use combustion so widely. Just imagine if the combustion of carbon had produced some godforsaken toxic substance (in addition to carbon dioxide) as a by-product. Making energy from combustion would then have turned into a woefully expensive activity, with special facilities required to sequester the poisonous waste. This would likely have radically altered the global production and distribution of energy, and human development would have been decidedly hampered. We may then have been forced to pick alternative sources of energy early on in our history, and the face of politics, economics, and technology would consequently have been very different.

Moving on, we come to what’s almost universally regarded as a villain these days—carbon dioxide. If carbon dioxide were harmless, we would live in a very different world. Sadly it’s not, and its properties again underscore the profound influence that a few elementary facts of physics and chemistry can have on our fate. The one property of carbon dioxide that causes us so much agony is the fact that it’s opaque to long-wavelength infrared radiation and absorbs it, thus warming the surroundings. The issue has divided the world like no other, and we still haven’t grasped its full consequences. But whatever they are, they will profoundly alter the landscape of human civilization for better or worse.

None of this would have mattered if it weren’t for the most important fact: Combustion produces energy. Energy production from the reaction is what drives life and human greed. We stay alive by eating carbon-rich compounds, which are then burned in a spectacularly controlled and efficient manner to provide us with energy. It is the all-important energy term in the combustion equation that has made life on Earth possible.

The same term of course is responsible for our energy triumphs and problems. Fossil-fuel-burning plants are nowhere as efficient in extracting energy from carbon-rich hydrocarbons as our bodies, but what matters is whether they are cheap enough. It’s primarily the cost of digging, transporting, storing, and burning carbon that has dictated the calculus of energy. Whatever the consequences of climate change, one thing will never change: We will continue to pick the cheapest fuel. Considering its extraordinarily fortuitous properties, this cheapest fuel will likely remain carbon for the foreseeable future. We will simply have to find some way to work around, over, or through its abundance and advantages to pave our way toward a sustainable, peaceful, and energy-rich future.

 
Chemical & Engineering News
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