Reactivity Series: Thermal Decomposition

How does thermal decomposition occur?

[heat] + metal carbonate → metal oxide + carbon dioxide

How does reactivity affect the difficulty thermal decomposition?

More reactive metal → more thermally stable carbonate → more difficult to decompose (cannot be applied the other way round)

What occurs when K2CO3 is heated and why?

• Unaffected by heat

• Colour before and after heating is white

• K is higher up in the reactivity series and is hence very stable to heat

What occurs when Na2CO3 is heated and why?

• Unaffected by heat

• Colour before and after heating is white

• Na is higher up in the reactivity series and is hence very stable to heat

What occurs when CaCO3 is heated and why?

CaCO3 (s) → CaO (s) + CO2 (g)

• Colour before and after heating is white

• Lower in the reactivity series and hence less stable to heat

• Fairly easy to decompose

What happens when MgCO3 is heated and why?

MgCO3 (s) → MgO (s) + CO2 (g)

• Colour before and after heating is white

• Lower in the reactivity series and hence less stable to heat

• Fairly easy to decompose

What happens when ZnCO3 is heated and why?

ZnCO3 (s) → ZnO (s) + CO2 (g)

• Colour before heating is white, after heating is yellow when hot, white when cool

• Lower in the reactivity series and hence less stable to heat

• Fairly easy to decomposel

What happens when FeCO3 is heated and why?

FeCO3 (s) → FeO (s) + CO2 (g)

• Colour before heating is green, after heating is white

• Lower in the reactivity series and hence less stable to heat

• Fairly easy to decompose

What happens when PbCO3 is heated and why?

PbCO3 (s) → PbO (s) + CO2 (g)

• Colour before heating is white, after heating is yellow

• Lower in the reactivity series and hence less stable to heat

• Fairly easy to decompose

What happens when CuCO3 is heated and why?

CuCO3 (s) → CuO (s) + CO2 (g)

• Colour before heating is green, after heating is black

• Lower in the reactivity series and hence less stable to heat

• Fairly easy to decompose

What happens when Ag2CO3 is heated and why?

2Ag2CO3 (s) → 4Ag (s) + O2 (g) + 2CO2 (g)

• Colour before heating is yellow, after heating is pale grey

• AgO produced is thermally unstable so it further decomposes to form Ag and O2