thermal decomposition

• thermal decomposition involves using heat to break down compounds.

  It is an endothermic process

   

  The more stable a compound is the more energy is required to break it down.
• What are the factors affecting thermal stability?

  group 1 and 2 nitrates and carbonates are different from compounds.

  • Compound are thermally very stable due to strong electrostatic forces between the positive and negative ions. And so they only melt.

   

  instead of melting like compounds, lithium and group 2 nitrates and carbonates will decompose (or break down) when heated.
• Thermal decomposition of metal oxides - Metal + Oxygen
• Thermal decomposition of metal hydroxides - Metal + Water vapour
• Thermal decomposition of nitrates

  decompose to produce a nitrite or oxide on heating

   

  Other products will be oxygen and/or nitrogen dioxide (NO2 = brown fumes)

   

  If the nitrate contains water of crystallisation, then steam will also be produced.
• Thermal decomposition of the nitrates

  A) brown fumes

  B) no brown fumes

  C) brown fumes

  D) greater decomposition

  E) lesser decomposition

  F) greater decomposition

  
• Thermal decomposition of the carbonates:

   

  Lithium carbonate and the group 2 compounds decompose to produced the oxide and carbon dioxide

   

  This becomes more difficult going down the group because they become more thermally stable (same reason as nitrates)
• thermal decomposition of the carbonates

  A) decomposition

  B) no decomposition

  C) decomposition

  
• greater decomposition occurs when:

  • cation has 2+charge
  • cation has a 1+ charge and is the smallest of group 1(ie Li+)
• the trend increases down the group due to the size of the cation, the cation gets bigger and this means they have a lower charge density as you descend the group.