When we see a smoke stack pumping waste into the air, it’s easy to see that something is happening. Black stuff is definitely flying out of the chimney! Smoke is pretty easy to look at, even if it’s not particularly easy to actually grab ahold of. In contrast, the Earth’s atmosphere itself is sometimes hard to think about, especially for people that don’t understand chemistry, or haven’t played with a vacuum sealer.
It took people a long time to understand that air was made of matter, and that air was different from space. Making a vacuum is not that easy; that was an important scientific discovery. It’s difficult to think of air for what it is: a low-density fluid made up of several different chemicals.
Oxygen is one of our favorite air chemicals because we die pretty quickly without it. But nitrogen and carbon dioxide are important too. The nitrogen and carbon in the food we eat comes from the air. The only major atmospheric gas we don’t eat is argon.
The ironic thing about our reliance on oxygen is that it’s one of the most dangerous chemicals around. There aren’t many things that oxygen won’t eventually wreck (react with). Most of those things are basically pre-wrecked (they already contain oxygen). Oxygen can ruin every part of a typical cell. In humans, the only oxygen-resistant parts I can think of are teeth and bones, and these both contain a lot of oxygen.
Each time you see a fire, the driving force behind the fire is the reaction of oxygen with the fuel. Oxygen is really what pushes your car forward because it changes a small volume of fuel into a large volume of hot gases. The gasoline is relatively incidental (could be replaced with alcohol or propane, for example). The heat and fuel create a type of chain reaction where the oxygen gobbles everything up, leaving oxidized carbon and hydrogen to mix into the atmosphere.
The oxidized hydrogen I mentioned is quite familiar: it’s dihydrogen monoxide. The water vapor enters the atmosphere, and often condenses into a cloud droplet. This is important for atmospheric thermal physics because water has a high heat capacity and cloud droplets block sunlight (leading to a cooling of the Earth’s surface).
Heat capacity is definitely an important concept. The statement that liquid water has a larger heat capacity than nitrogen gas means that a kilogram of water droplets has more heat than a kilogram of nitrogen, at a given temperature. So understanding heat capacity requires an understanding of how molecules store heat. We’ll tackle that next time.
Ryan MB Hoffman has a B.Sc. in Biochemistry from Queen’s University in Kingston, Ontario, and a Ph.D. in Biochemistry from the University of Alberta in Edmonton, Alberta. He is mostly interested in how protein molecules fluctuate throughout their functional processes. During his doctoral work he studied troponin, which is a switch that regulates striated muscle contraction. He works as a post-doctoral scholar at the University of California, San Diego, at the Center for Theoretical Biological Physics. He is active with the Intrinsically Disordered Proteins subgroup of the Biophysical Society. Ryan likes to remind people that his contributions to TRN are performed entirely using his personal resources.