Chemical Changes

• In a chemical reaction, atoms are rearranged to form new substances with different properties.
• We cannot see chemical bonds, but we can view signs of chemical changes.
• Chemical changes occur when substances react with each other, resulting in the formation or breaking of chemical bonds
• Indicators of chemical changes include:

  • Light emission
  • Gas production
  • Precipitation (solid is produced)
  • Color change
  • Temperature change
• During the reaction of magnesium with oxygen, changes observed include:

  • Formation of magnesium oxide (MgO)
• Iron or steel corrodes when they react with oxygen and water
• This process is known as rusting
• The metal becomes weaker over time and eventually all of it may become metal oxide
• Ways to prevent iron from rusting:

  • Introduce a physical barrier to oxygen and water
  • Examples include painting with oil-based paint, oiling/greasing, and coating with plastic
• Rusting can also be prevented by:

  • Alloying (mixing iron with chromium to make stainless steel)
  • Galvanising (coating with zinc)
  • Electroplating (coating with gold, silver or copper)
• Corrosion reaction is what caused the Statue of Liberty to turn green.
• Copper reacts with sulfur dioxide in air pollution to form copper(II) sulfate which gives off blue colouration.
• When corrosion happens, rust appears on the metals' surface.
• Corrosion is what weakens the metal (and potentially makes it dangerous/dirty) over time.
• Iron requires water/moisture and oxygen to rust.
• The chemical formula of rusting

  Iron + Oxygen + Water -> Hydrated iron(III) oxide