ELI5: If carbon is a byproduct\end product of combustion, why exactly is coal so good at burning? Isn't coal just pure carbon?
ChemistryNope! Coal is carbon bonded in chains with hydrogen and oxygen (and a few other, kinda problematic things like sulfur) when burned, the bonds keeping all that together are broken, creating water, carbon di/monoxide, and freeing whatever other chemicals were in the coal, like calcium and sulfur.
Bituminous coal has a composition of about 84.4% carbon, 5.4% hydrogen, 6.7% oxygen, 1.7% nitrogen, and 1.8% sulfur, on a weight basis.
Adjusted for molar mass that's 7:5:0.5:0.12:0.06
So for every seven hundred atoms of carbon, there's five hundred hydrogen. Fifty oxygen, twelve nitrogen, and six sulfur atoms.
Traditional chain structures are closer to 2:1 hydrogen to carbon, such as sugar at 11:6. Coal is not mostly long hydrogenated chains, though it will contain lots of them for sure. Coal is mostly carbon bonded to just other carbon.
Carbon dioxide is a byproduct of complete combustion. It’s just often referred to as “carbon” when talking about pollution, or even the carbon cycle.
Pure carbon is a product of incomplete combustion. You get CO2 either way.
Coal is basically a hydrocarbon the active molecule contains hydrogen, carbon and oxygen all bound up together in a similar fashion to sugar and like sugar when it is "burned" it releases energy converting the hydrocarbon to carbon dioxide and water.
Combustion reactions require a fuel (this being the carbon in the coal) and an oxidizer (usually oxygen). You break the C-C bonds to form CO2 as well as water, which gives off energy
Also coal isn’t just carbon, it’s also oxygen and hydrogen.
Carbon comes in many forms. Some have considerable potential energy stored in bonds, while others at the bottom of the potential energy scale.
Chemically speaking, “reduced” carbon has high energy bonds. Carbon bonded to hydrogen or other carbon is very reduced. Coal, oil, graphite and diamonds are examples of chemicals with very reduced carbon, and a lot of potential energy which can be released by combustion.
At the other end of the scale is “oxidized” carbon such as carbon dioxide and carbon monoxide, where carbon is bonded to oxygen. These molecules are stable because there is no potential energy left in the molecular bonds.
Sugars are the compounds made when plants convert oxidized carbon (CO2) to reduced carbon, using the energy from light. Sugars have carbon-hydrogen bonds and carbon-carbon bonds, but also retain some carbon-oxygen bonds, and are intermediate in potential energy. However, the potential energy in sugars can be converted and concentrated into fats and oils.
Coal is mostly carbon (C). When carbon burns it merges with oxygen (O2) in the air to create carbon dioxide (CO2) which we refer to as "carbon" for short.
Carbon Dioxide is a byproduct of combustion, which forms when carbon-based compounds oxidize (burn).
Carbon (C) came come in different flavours. Pure carbon can burn. Burning means reacting with Oxygen (O). Carbon and Oxygen become CO2. Pure carbon is not the end produce of combustion but CO2, which is sometimes incorrectly called Carbon in some cases.
For starters, what you're thinking of is charcoal, which is the result of wood being heated -not burned, really- in a low-oxygen environment. Now, coal and other fossil fuels are all hydrocarbons, meaning chains of hydrogen and carbon and usually some orher groups mixed in as impurities- nitrogen groups, alcohol groups- and when they burn the oxygen, simply, reacts with carbon to form CO2, carbon dioxide; and hydrogen to form H2O, water vapor. Carbon can conceivably react with oxygen to form CO2, but understand that when elements and compounds react to form new compounds, the release of energy comes from the fact that those new products are more stable than the reactants. CO2 (and H2O) are more stable than O2 or whatever hydrocarbon chains that were combusted, and so it releases energy.
Carbon dioxide (CO2) is a product of combusion. It isn't pure carbon, it's a greenhouse gas. The term "carbon dioxide" is shortened to just "carbon" when talking about global warming.
Soot is a form of impure carbon that is a product of incomplete combustion of hydrocarbons (molecules composed mostly of carbon and hydrogen, such as paraffin, alcohol, kerosene, etc.).
Pure carbon that hasn't yet reacted with anything can react (burn) in the presence of oxygen. Coal isn't pure carbon either, however, it's mostly carbon but it includes other compounds that burn (made mostly of hydrogen, sulfur, oxygen, and nitrogen), often releasing pollutants when they react.