Why are carbon and it's compounds used as fuels
Answers
The life on Earth is carbon based. Which means carbon gets into a complex cycle where it is formed and converted to different compounds. In other words, it is recycled. And it is available in plenty around us.
It is readily available. In the form of a dead tree or dug up from the ground. One can collect the fuel required from the surroundings without depending on complex machineries or technologies.
Carbon fuels are highly versatile. It can boil water and melt steel. The temperature control is very easy.
Above all, it requires a fairly low temperature to start the burning or combust. The heat from two stones rubbed together served the early humans and the press of the plunger in a gas lighter serves the modern humans. It is easy to start and control a fire using carbon.
We can use hydrogen as a fuel, aluminium, magnesium, or anything that can react and release heat is a fuel. But none of them will have the advantages of carbon. Got Hydrogen you will need electricity for producing the gas. Storage and transport is complex, and there is a potential for accidents all the time. Similarly for others too, the complexities are more.
Carbon is unusual in that it can make 4 covalent bonds and it can make bonds with itself while still having room to bond to other atoms. This allows carbon based molecules to grow to enormous size compared to other molecules. These large molecules store large amounts of energy compared to smaller molecules with fewer bonds. One of the reactions that carbon based molecules can do to release energy is react with oxygen, a free, and ubiquitous reactant that we don’t need to actively add in most environments on earth. By weight and atom count, it’s actually not the carbon atoms that are the most abundant reactants in these combustion reactions but oxygen.
You could think of carbon compounds as being really efficient at releasing the energy stored in oxygen for a different, but accurate, perspective of what’s going on.
It’s a combination of having high energy density, convenient handling and storage characteristics, relatively low toxicity both before and after burning, widespread low-cost availability, rather low activation energy, and fairly low risk of catastrophic explosion or other accidents during common usage scenarios.
Carbon has 4 valence electrons, which means 4 “empty slots” for other things to bond to. It seems to love hydrogen, as you can get everything from methane to 20+-carbon-chain alkanes to burn, though the sweet spot for gasoline seems to be octane (8 carbon chain).
The C-H bond itself isn’t the most energetic, but there are a *lot* of them in something like gasoline and they’re fairly easy to break apart (oxidize) in a controlled manner. Per weight, these small and medium-chain hydrocarbons have excellent energy density. They’re pretty easy to acquire and store compared to something like pure hydrogen or U-235, too, and the byproducts are far less immediately lethal than the burst of neutrons and radioisotopes you’d get out of nuclear fuel.
Hydrocarbons aren’t the best fuel by a pure energy density metric, but they’re not bad, and all their other characteristics come together in ways that make it overall a good choice purely from the perspective of convenience.