Oxidation of Phosphorus Phosphorus spontaneously combines with oxygen in the atmosphere

Demonstration  The lump of phosphorus burned with no outside initiation, demonstrating a combustion reaction  The film of phosphorus did not burn but glowed, demonstrating photoemission

Purpose  To observe a combination reaction involving phosphorus and atmospheric oxygen  To compare the behavior of a lump of phosphorus to a thin film of phosphorus

Concepts 1.Combination Reactions 2.Reaction Kinetics 3.Photoemission

1.Combination Reactions  In both demonstrations phosphorus combines with oxygen from the atmosphere  Combination reactions have the general form A+BC  The chemical equation is P 4 +5O 2 P 4 O 10  the reaction is exothermic  the name of the product is tetraphosphorous pentoxide

2.Reaction Kinetics  Since both demonstrations involve the same chemical reaction they both are exothermic  Since in the lump the phosphorus is not dispersed the heat of reaction is intense enough to speed the reaction and to cause the lump to burst into flame  When the phosphorus is spread thinly the heat dissipates and photoemission is able to be observed

3.Photoemission  The emission of light by a substance  In this demonstration it is a greenish glow  Caused by a substance in the excited state having high energy electrons giving off visible energy when the electrons return to the ground state

Conclusions  The concentration of a compound influenced the rate at which it reacted  Different effects were observed depending on the concentration  combustion or  photoemission

Comments  The phosphorus was dissolved in a solvent then dispersed in mineral oil before spreading  The intermediate species responsible for photoemission is PO which is ultimately converted to P 4 O 10