Question

Why do substances burn with or without flame

Answer 1

Flame (fire) is the effect of a chemical reaction that produces visible light and heat. The chemical reaction is going on in the substance being burned, and in the air above it as the heat of combustion vaporizes some of the substance being burned.eg. kerosene Oil. Those substance s which do not vaporize during burning do not form flames eg. Charcoal, Sugar, etc.

Answer 2

Flame is on produced when the substance vaporizes on heating and the vapours catch fire .But some substances like coal does not vaporizes so the flames are not produced while burning