Question

Something that burns is said to be flammable. Do you think steel wool is flammable? is it readily flammable in air? in oxygen? what sort of differences to you observe?

Answer 1

Answer

Yes, Steel wool is flammable. Let see, the reason.

Here, the surface area plays a major role. The surface area of steel wool is more when compare to the surface area of a steel block/rod. Since the steel wool is made up of thin fiber of steel, the surface is more which helps the iron atoms to be contact with the oxygen molecules in air. When we introduce a heat source to the steel wool, the iron atoms get energy to react with the oxygen molecules. Iron atoms combine with oxygen and form iron oxide (FeO₂). The metallic bonds of the steel wool and the covalent bond of oxygen molecule (O₂) were break down and create a new covalent bond between iron & oxygen (iron oxide). This is a self-sustained and an exothermic (exo-out, thermic-heat) reaction, repeated again and again after initiation and thus becoming a chain reaction. This chain reaction heats up to 700 degree Celsius. The greater surface area to volume ratio of steel wool allows it to react with oxygen molecules in air and thus the steel wool become a flammable material.

Air is a mixture of many gases which contains only 20.9% of oxygen in it. So the above reaction is actually a slow reaction in the presence of air. But in a pure oxygen environment, the same reaction is even more violent and it burns the steel wool very fast. When we consider a steel block or rod, the surface area to volume ratio is so less and there is no chance for the reaction between iron atoms and the oxygen molecules. Therefore, the steel wool is flammable and steel block is non-flammable.