Question

Burning of carbon is exothermic process, yet it does not start on its own. Explain.

Answer 1

The reaction of carbon and oxygen i.e. combustion doesnot start with it's own because of the activation energy. Activation energy is the energy input required to start dissociation of carbon and oxygen.

Once enough energy is introduced to initiate the formation of carbon dioxide, enough energy is released to sustain the reaction.

If the “activation energies” are low enough, some substances will ignite and burn spontaneously on contact with oxygen at room temperature, examples are sodium, yellow phosphorus.