The Chemistry of Combustion
Greetings! Let’s brush up on chemistry. We’ll need it!
An atom is, “the smallest unit into which matter can be divided without the release of electrically charged particles” (https://www.britannica.com/science/atom). It consists of positively charged protons and neutral neutrons in a nucleus (center) surrounded by a cloud of negatively charged electrons.
Powerful attracting forces between protons and electrons maintain atomic cohesion. The majority of an atom’s mass is concentrated in the nucleus, but the electrons have massive orbits. If the nucleus were scaled up to the size of a basketball, its electrons would orbit two miles away! Atoms are roughly the same size, regardless of the number of electrons. Electrons exist at higher or lower energy states, populating different orbital “shells” surrounding the nucleus. Higher energy = electrons in the largest shell farthest from the nucleus, lower energy = electrons in the smallest shell closest to the nucleus.
The periodic table is extremely useful. The atomic number describes how many protons (and therefore electrons) are present in the atom. Hydrogen has one proton, one electron, and one neutron. Thus, the atomic number is 1. Atomic weight is a different metric. Atoms can have different numbers of neutrons in their nucleus. We call these atoms isotopes. A hydrogen isotope with 2 neutrons is called deuterium, and with 3, tritium. Deuterium and tritium have higher atomic weights than hydrogen because they contain extra particles (neutrons).
When we’re ready to explore climate proxy records hundreds of millions of years old, we’ll need to understand oxygen isotopes, specifically O16 (“oxygen-16”, which has 8 protons and 8 neutrons) and O18 (“oxygen-18”, which has 8 protons and 10 neutrons). Ditto for other elements and their isotopes. For now, I digress.
Molecules form when atoms share electrons. One pair of shared electrons = one bond. Atoms that don’t have equal numbers of protons and electrons to maintain a neutral charge are called ions. Cations are positively charged while anions are negatively charged.
Oxygen has 8 protons, and so is stable when 8 electrons populate its orbital shells. To form a water molecule (H2O), an oxygen atom forms two single, covalent bonds with two hydrogen atoms by sharing 4 total electrons: 2 from the oxygen atom, and 1 from each hydrogen atom. Hydrogen only has one electron to share, so it can only form a single bond with one other atom, often carbon or oxygen. Some molecules have double or triple bonds (i.e. 4 or 6 electrons are shared in each bond). Nitrogen often forms a very stable triple bond with other nitrogen atoms.
It’s important to mention here that phase changes (moving from solid, to liquid, to gas) do not cause any separation within a single molecule: a molecule of water remains one oxygen atom bound to two hydrogen atoms no matter whether it is ice, water, or steam. Phase changes refer to the degree of inter-molecular movement (movement between molecules): ice molecules are frozen in place arranged in a crystal structure, liquid water molecules are hydrostatically attracted to each other but pass by easily, and vapor molecules are spread so far apart that they expand to the volume of whatever container they fill.
Hydrocarbons are hydrogen bonded with carbon. All fossil fuels are hydrocarbons, and they are packed full of energy for precisely this reason! The burning of fuel, or combustion, is an oxygen-adding, heat-releasing reaction between a fuel and an oxidant. Combustion of hydrocarbons would be written in the following equation:
2C8H18(1) + 25O2(g) —> 16CO2(g) + 18H2O(g)
Hydrocarbons + oxygen = carbon dioxide + water. In every reaction, mass must be conserved, meaning there will be the same number of atoms on both sides of the equation. You’ll notice the equation is balanced and there remain 16 carbon atoms, 36 hydrogen atoms, and 50 oxygen atoms at the end, thus maintaining the Law of Conservation.
Methane is CH4. Propane is CH3CH2CH3. Coal is C135H96O9NS (it’s 85% carbon by mass). CO2 is the inevitable product of fossil fuel combustion. To argue otherwise is to rage against Nature, against the unfolding of reality.
Only by understanding the problem can we solve it. We understand it. Now let’s solve it.
Thank you to my friend, Dr. Menger for her review and edits for several sentences. Having only achieved a B+ in college chemistry, I thought it best to consult someone who knows much more about the subject matter than I do. Congratulations, Dr. Menger on earning your PhD in Chemistry. You’re a rockstar.
Submit your climate questions to tjclimatecorner@gmail.com.
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