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Combustion of Magnesium in Carbon Dioxide


2 blocks of Dry Ice with hollows drilled out about 0.5 cm deep

Small bottle of Magnesium Turnings (about 10g)

Propane Torch

Thermal Gloves

Crucible Tongs

Gloves and Goggles



  1. There are two dry ice blocks with identical cavities in them.
  2. Fill one cavity about half full with magnesium filings.
  3. Holding the covering block with one hand, light the filings with the torch.
  4. Cover burning magnesium with the other block, making sure the cavities line up.
  5. Dim lights.
  6. After the Mg stops burning, drop the residue out and break it open.
  7. The class usually wants an instant replay


2Mg + CO2 --> 2MgO + C

Standard heat of reaction is -809kJ.

The black residue is a mixture of carbon and magnesium nitride, Mg3N2.


Waste Management

Once cool, the carbon residue can be thrown in the trash.


Note: Do this in a well ventilated room  - I have set the fire alarm off with the haze generated from this demonstration.