Burning magnesium, Mg in 100% pure oxygen very cool demo!
This is a combustion reaction taking place between oxygen and Mg. The Mg must first be heated very strongly in order to meet the activation energy for this reaction. 2Mg + O2 = 2MgO Safety note: Mg burns with a bright flame which also gives out UV light. Do not stare directly at the light if you are intending on doing this practical.
