Why Carbon and Its Compounds Are Used as Fuels

CH4 + 2 O2  ->  CO2 + 2 H2O + heat
C + O2      ->  CO2 + heat

#2. They have high calorific values

Fuel	Calorific value (kJ/kg)
Methane / natural gas	~55,000
LPG	~55,000
Petrol	~45,000
Kerosene	~43,000
Charcoal	~30,000
Coal	~25,000–33,000
Wood	~17,000–22,000

Even at the bottom of this table, wood delivers far more heat per kilogram than most non-carbon alternatives available at similar cost.

#3. They burn in ordinary air

Carbon compounds react with atmospheric oxygen at accessible temperatures. No exotic oxidiser is needed, no special atmosphere, no containment beyond ordinary appliance design.

This sounds trivial until you consider alternatives. Many substances release more energy per kilogram in some reaction or other, but require an oxidiser that must itself be manufactured and carried — which is why rockets carry liquid oxygen and cars do not.

#4. They exist in all three states

State	Fuel	Best suited to
Solid	Coal, charcoal, wood	Bulk industrial heat, steel making, static plant
Liquid	Petrol, diesel, kerosene	Transport, where energy density per litre matters
Gas	Natural gas, LPG, biogas	Domestic cooking and heating, clean controllable flames

This range is unusual and extremely useful. A single family of compounds supplies a dense pumpable liquid for aircraft, a clean controllable gas for a kitchen, and a cheap bulk solid for a power station.

#5. They are abundant

Carbon compounds are available as coal, petroleum, natural gas, wood, agricultural waste and biogas. Carbon is the fourth most abundant element in the universe by mass and forms an enormous variety of stable compounds — a property called catenation, its unusual ability to bond to itself in chains and rings.

That structural versatility is why carbon supports millions of compounds while most elements support a handful, and why the fuel family is so broad.

#6. Storage and transport are straightforward

Carbon-based fuels are chemically stable at ordinary temperatures. Petrol stored for a year is still petrol. They can be pumped, piped, shipped, poured and carried, and they do not self-discharge the way a battery does.

Compare hydrogen: higher calorific value, but requiring 700 bar compression or cryogenic cooling, and embrittling the metals used to contain it.

#7. The products are gases that leave by themselves

Complete combustion produces carbon dioxide and water vapour, both gases at flame temperature. They flow out of the appliance without needing to be cleared, unlike ash, which must be physically removed.

Gaseous and liquid carbon fuels leave essentially no residue at all — a large part of why gas replaced coal in kitchens.

#The disadvantages, stated plainly

The same chemistry that makes carbon compounds useful causes the problems:

• Carbon dioxide is an unavoidable product of complete combustion, and it is the principal greenhouse gas.
• Carbon monoxide and soot appear whenever the oxygen supply is inadequate.
• Sulphur dioxide comes from sulphur impurities in coal and heavy oils.
• Non-renewable for fossil-derived carbon compounds, though biomass and biogas are renewable.

None of this contradicts the reasons above. Carbon compounds are used as fuels because they are exceptionally good at being fuels; the costs are attached to that same property, which is why the search for alternatives is difficult rather than obvious.

The same chemistry produces the problems: carbon dioxide and the other disadvantages, and carbon monoxide and soot when the air supply is short.

#The compact answer

Carbon and its compounds are used as fuels because they burn in air with the release of a large amount of heat, giving them high calorific values. They are readily available as coal, petroleum and natural gas, exist as solids, liquids and gases suited to different uses, leave little ash on burning, and are easy to store and transport.