Question

Why are most non-renewable energy resources burned?

Answer 1

It is the process of breaking the hydrocarbons into carbon-dioxide and water-vapour, that releases energy. That is why most non-renewable energy sources are burnt.

Explanation:

Hydrocarbons `C_NH_{2(N+1)}` represent a state of high electrostatic potential energy. In nature it is observed that almost all system tend to proceed toward a state of lower potential energy. High potential energy states are thus inherently unstable and systems would reconstitute themselves releasing the energy if they can settle in a new state of lower potential energy.

Most non-renewable energy sources are fossilised organic matter.
Deep under the Earth's surface where the temperature is found in the range of `100^oC - 150^oC`, organic matter (kerogen) undergo thermal decomposition progressively over geological time periods to lighter hydrocarbons like methane, through a process called Catagenesis . The final product is simple hydrocarbons like Methane.

Methane has four hydrogen atoms bound to a carbon. There is electrostatic potential energy associated with these bonds. Now if oxygen molecules come along they provide an opportunity for the hydrogen-carbon-oxygen atoms to reconfigure themselves to go to a state of lower potential energy. But for this to happen there has to be some initial driving energy. This is provided by a fire/spark. Once it is initiated the energy released in the reconfiguration of one set of molecules is sufficient to keep the reaction going. So it is the process of breaking hydrocarbons to carbon-dioxide and water vapour (burning) that releases energy. So if we want energy from hydrocarbons we must burn it.