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Name: Joe V.
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: 
10/14/2004



Question:
A text book question says CaCO3 burns with O2 to form CaO and CO2.... does it really burn, or just decompose with heat. If it burns, what is the balanced equation?


Replies:
I think you are right in suspecting that CaCO3 does not undergo combustion, I do not even think that it undergoes decomposition under most laboratory conditions. I know that in my labs, we use a mixture of MgCO3 and CaCO3 (to simulate dolomite) and count on the fact that we can decompose MgCO3 with a bunsen burner, but the CaCO3 remains intact.

Greg (Roberto Gregorius)


Joe,

CaCO3 does not combust, by the definition of the word. It is "converted" into lime (CaO) by a thermal decomposition reaction. This IS a reversible reaction. When the calcium carbonate is heated to around 932 F, it will liberate a CO2 molecule and will become CaO. This, demonstrated as a one way reaction is shown as;

CaCO3 + HEAT (932 F) == CaO (lime) + CO2.

I do not know the exact mechanism of this decomposition. Nor do I know how, exactly, the CO2 would combine with lime (CaO) to go back to its original CaCO3. But I have read that it is a reversible reaction.

Thanks for the question.
Darin Wagner


Joe- you seem to have the correct understanding. It just decomposes with heat.

CaCO3 <--> CaO + CO2.

In either state, both carbon and calcium are fully oxidized, cannot hold any more oxygen atoms.

Jim Swenson


I believe that CaCO3 decomposes when heated to form CaO and CO2 without the need of any additional O2. This is not combustion in the usual sense of the term.

Vince Calder



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