What is a hydrocarbon and why is it important to fossil fuels?

• A. A hydrocarbon is a compound of hydrogen and carbon, with energy stored in covalent bonds.
• B. A hydrocarbon is a compound of oxygen and carbon, with ionic bonds.
• C. A hydrocarbon is a metal-carbon alloy.
• D. A hydrocarbon is a mixture of hydrogen and helium.

Answer: (A)

A hydrocarbon is a molecule made entirely of hydrogen and carbon, with the energy stored in covalent bonds between those atoms. This bond energy is why fossil fuels release so much heat when burned: breaking the carbon–carbon and carbon–hydrogen bonds releases a large amount of energy that can be converted into motion, electricity, or heat. Fossil fuels—the main examples being coal, oil, and natural gas—are rich in hydrocarbons formed from ancient organic matter. Their high energy density and the ability to release energy efficiently when combusted explain why hydrocarbons are central to our energy system. The other descriptions—oxygen-containing compounds with ionic bonds, metal–carbon alloys, or mixtures of hydrogen and helium—do not describe hydrocarbons.