The Chemistry of Combustion
Combustion of hydrocarbons, aka fossil fuels, inevitably leads to the creation of carbon dioxide.
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.
Image sourced from: https://study.com/academy/lesson/what-is-hydrocarbon-definition-formula-compounds.html
Systems Thinking: Unlocking A Complex Earth
Earth is full of complex intricacies, different spheres interacting in nonlinear ways, shaping our lived experience as delicate humans in a planetary-scale system.
July 28th, 2021
Earth is a complex, multi-system wonder! Just as the human body consists of multiple systems that all work in tandem to sustain human life, the Earth System is composed of multiple systems that sustain a vast quantity and variety of life forms. These subsystems are: the lithosphere, also called the geosphere (rocks, soil, molten rock, fossil fuels), the hydrosphere (oceans, rivers, lakes, groundwater, etc.), the atmosphere (tropo-, strato-, meso-, thermo-, magneto-, and exo-sphere), the biosphere (oceanic and terrestrial plants and animals), and some climatological conventions separate out the cryosphere (ice and snow).
To understand how the Earth System operates, we need to understand “systems thinking”. It helps to break Earth down into “stocks” (nouns) and “flows” (verbs). A stock/reservoir is any entity that can be filled or depleted, like a bathtub filling or draining. We just listed the Earth System stocks: the lithosphere, hydrosphere, biosphere, atmosphere, and cryosphere. We concern ourselves with how materials and energy flow throughout the system, i.e. how water, nitrogen, carbon, phosphorous, and other elements of key interest move throughout the different spheres. This means that the flows/fluxes are actions, or processes through which materials can move from one sphere to another.
Most of us confidently understand the hydrological cycle. Evaporation is the flux that moves water from the hydrosphere and lithosphere (in the form of soil moisture) up into the atmosphere. Precipitation is the flux that moves water back down from the atmosphere to the hydrosphere and lithosphere. Condensation is another flux/process in the hydrological cycle, but in this example, it does not transfer water from one sphere to another, but occurs solely within the atmosphere.
Systems Thinking also requires us to understand residence times and time lags, nonlinear relationships, as well as feedback loops. Residence times refer to how long a material remains within a stock. Sticking to our hydrological cycle example, here’s how long a water molecule stays, on average, within a given stock: Oceans/Seas (at a depth of 2,500 m) 4,000 years, Lakes/Reservoirs 10 years, Swamps 1-10 years, Rivers 2 weeks, Soil Moisture 2 weeks-1 year, Groundwater (120 m) 2 weeks-10,000 years, Ice Caps/Glaciers 10-1,000 years, Atmospheric Water 10 days, Biospheric Water 1 week (https://www.spokaneaquifer.org/the-aquifer/what-is-an-aquifer/residence-time-of-groundwater/).
For each of the cycles we’ll cover (rock, carbon, nitrogen, etc.) there will be different residence times for the material of interest. I cannot over-emphasize how important it is to consider the residence time of a given material. For some cycles, the residence time is hundreds of millions of years!
The lag time we experience every day is the diurnal (daily) temperature lag. Noon is when we receive the most sunlight, but peak daytime temperatures occur several hours after noon. That’s because air warms (and cools!) faster than water, dirt, and rock. The earth continues to radiate heat well past noon, maintaining warm temperatures. Another example is seasonal ocean temperatures: northern hemisphere oceans tend to reach their warmest temperature in August and September, 2-3 months after the summer solstice! (https://www.seatemperature.org/atlantic-ocean). This is due to the massive heat capacity of water: it takes 4,184 joules to warm 1 kilogram of water by 1°C (by comparison, it takes 385 joules to warm 1 kilogram of copper 1°C) (https://www.usgs.gov/special-topic/water-science-school/science/specific-heat-capacity-and-water?qt-science_center_objects=0#qt-science_center_objects). Thus, the ocean continues to warm well beyond the longest day of the year.
Exponential growth is the most crucial nonlinear relationship to understand in the Earth system. Human population is one example: it took about 12,000 years to reach 1 billion people (in the year 1800), and then it only took 120 years to grow to 7.9 billion (https://ugc.berkeley.edu/background-content/population-growth/).
Lastly: feedback loops. Positive feedback loops amplify or increase the effect of a forcing, negative feedback loops dampen or decrease the effect of a forcing. A positive feedback: as sea ice melts, dark ocean water is revealed. Dark ocean water absorbs sunlight (as opposed to reflective white ice and snow), and so absorbs more heat, which melts more ice, on and on and on. Right now, permafrost in the arctic is melting and releasing methane, a greenhouse gas 30 times more powerful than CO2 but with 1/10th the atmospheric residence time (https://royalsocietypublishing.org/doi/10.1098/rsta.2014.0423).
This heats the planet, which melts more permafrost, which releases more methane, etc. Same with wildfires: combustion moves carbon from the biosphere to the atmosphere, and the train runs away.
Canary in the coal mine? Or arctic tern on the burning permafrost graveyard . . .?
Image sourced from: https://ugc.berkeley.edu/wp-content/uploads/2016/01/Human-Pop-Growth-2019.jpg