Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Burning Calcium Carbonate
Name: Joe V.
Status: educator
Age: 30s
Location: N/A
Country: N/A

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?

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)


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

Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory