Combustion of Magnesium and Burning Steel Wool

This is part of the HSC Chemistry course under the topic Factors that Affect Equilibrium

HSC Chemistry Syllabus

  • Conduct practical investigations to analyse the reversibility of chemical reactions, for example:

– burning magnesium

– burning steel wool (ACSCH090)

Combustion of Magnesium

  • Burning magnesium is an example of metal combustion reaction which is highly exothermic. It releases energy in the form of light and heat.

 $$2Mg_{(s)} + O_{2(g)} \rightarrow 2MgO_{(s)}\;\;\; \Delta{H}<0$$

Figure: burning a magnesium strip generates light energy. It is an irreversible process.

  • Flame (heat energy) is required to overcome the relatively small activation energy barrier of the reaction. 
  • Burning magnesium goes to completion (until magnesium strips are fully converted into magnesium oxide). It is an irreversible reaction because magnesium oxide is very stable at standard conditions. The activation energy of the reverse reaction (endothermic) is also much larger.


Burning Steel Wool

  • Similar to magnesium, burning steel wool (made of mostly iron) is an example of exothermic, irreversible reaction.

$$4Fe_{(s)} + 3O_{2(g)} \rightarrow 2Fe_2O_{3(s)}\;\;\; \Delta{H}<0$$

Burning steel wool is similar to burning magnesium. The formation of iron oxide is an irreversible process.


  • The activation energy of the reverse reaction is relatively large under standard conditions.

Previous section:  Practical Investigations of Le Chatelier's Principle (Nitrogen Dioxide and Dinitrogen Tetroxide equilibrium)

Next section: Calculating Equilibrium Constant (ICE Table)