CIE A Level Chemistry复习笔记2.2.3 Thermal Decomposition of Nitrates & Carbonates

• Thermal decomposition is the breakdown of a compound into two or more different substances using heat

Thermal decomposition of carbonates

• The Group 2 carbonates break down (decompose) when they are heated to form the metal oxide and give off carbon dioxide gas
• The general equation for the decomposition of Group 2 carbonates is:

The thermal decomposition of magnesium carbonate to form magnesium oxide and carbon dioxide gas

• Going down the group, more heat is needed to break down the carbonates

Thermal decomposition of nitrates

• The Group 2 nitrates break decomposed when they are heated to form the metal oxide, oxygen gas and nitrogen dioxide gas (which is a brown toxic gas)
• Since the formed nitrogen dioxide gas is toxic, the decomposition of nitrates is often carried out in a fume cupboard

The diagram shows the thermal decomposition of magnesium nitrate to form magnesium oxide, oxygen gas and nitrogen dioxide gas

• The general equation for the decomposition of Group 2 nitrates is:

• Going down the group, more heat is needed to break down the nitrates
  • The smaller positive ions at the top of Group II will polarise the nitrate ions more than the larger ions at the bottom of the group
  • The more polarised they are, the more likely they are to thermally decompose