The content of oxygen in air is ~20% by volume. Comparative experiments of the intensity of combustion (the rate of the combustion reaction) in air and in pure oxygen may show rather big differences.
In this experiment, the combustion of a piece of coal (charcoal, carbon) was comparatively demonstrated in air (barely noticeable glow) and in pure oxygen. When pure oxygen was passed over it, the piece of charcoal ignited with a bright flame:
C(s) + O2(g) → CO2(g)
1) RATE OF REACTION, EQUILIBRIUM: “Effect of concentration on reaction rate”
2) OXYGEN: “Preparation of oxygen”
4) NITROGEN AND AMMONIA: “Nitrogen as a fire extinguisher”