Magnesium is a silvery-white, lightweight metallic element found abundantly in the Earth’s crust and oceans. It is an essential component in many minerals, such as dolomite and magnesite. This element plays a role in lightweight alloys used in electronics, car parts, and aircraft construction due to its low density and high strength. Magnesium is also biologically significant, being central to the chlorophyll molecule in plants and required by numerous enzymes in the human body.
The Fiery Transformation
When ignited, magnesium undergoes rapid combustion with oxygen in the air. This reaction requires an initial heat source to overcome its activation energy, but once started, it releases significant energy. The burning magnesium produces intense, bright white light and generates substantial heat, reaching temperatures exceeding 2000 degrees Celsius. Approximately 10% of the energy released during combustion is emitted as light.
Magnesium’s reactivity allows it to continue burning even in environments typically used to extinguish fires. It can react vigorously with carbon dioxide, extracting oxygen atoms and leaving behind solid carbon deposits. This reaction demonstrates magnesium’s strong affinity for oxygen, even when bound within other compounds. Furthermore, if oxygen is depleted, burning magnesium can also react with nitrogen gas to form magnesium nitride. This highlights its unique chemical properties.
The End Product
The product remaining after magnesium burns is magnesium oxide (MgO). This material appears as a white, powdery ash, distinctly different from the original silvery, metallic magnesium. Magnesium oxide is formed as magnesium atoms lose electrons to oxygen atoms, creating an ionic bond. It is a highly stable ceramic material known for its excellent heat resistance and high melting point, around 2800 degrees Celsius.
Magnesium oxide is also noted for its high thermal conductivity and electrical insulation properties. This white powder is only slightly soluble in water, but it can react with water to form magnesium hydroxide. The formation of this new compound signifies a complete chemical change from the original magnesium metal.
Uses and Safety Considerations
The intense light and heat produced by burning magnesium have led to various practical applications. Historically, it was used in photography flashbulbs to create bright, instantaneous illumination. Today, it finds use in flares, fireworks, and sparklers, providing brilliant white light for signaling and entertainment. Magnesium’s vigorous combustion also makes it suitable for emergency igniters.
Despite its utility, burning magnesium presents significant safety hazards. The extreme brightness of the flame contains ultraviolet light, which can cause temporary or even permanent eye damage if viewed directly. The intense heat generated poses a risk of severe burns to skin and can easily ignite nearby flammable materials. Importantly, water should never be used to extinguish a magnesium fire.
The burning magnesium reacts violently with water, producing highly flammable hydrogen gas and intensifying the fire. Similarly, carbon dioxide fire extinguishers are ineffective and can worsen a magnesium fire because the burning metal can extract oxygen from CO2, fueling combustion and leaving behind carbon. Proper fire suppression for magnesium involves specialized methods, such as using Class D dry chemical fire extinguishers. Covering the burning magnesium with dry sand or a magnesium foundry flux can also smother the fire by depriving it of oxygen.