Final answer:
CaCO3 can be calcined under an environment with a CO2 pressure of 0.001 atm at 850°C. At this temperature, the decomposition of CaCO3 is favored, especially if CO2 is continuously removed from the system.
Step-by-step explanation:
Yes, CaCO3 can be calcined under an environment having pCO2 = 10⁻³ atm at 850°C. The decomposition of CaCO3 into calcium oxide (CaO) and carbon dioxide (CO2) is temperature-dependent, and at temperatures above approximately 700°C, measurable amounts of CO2 begin to form.
The equilibrium pressure of CO2 increases with temperature; around or above 835°C, the products of the reaction (CaO and CO2) are favored, hence equilibria are supposed to shift towards the products at high temperatures as per Le Chatelier's principle.
When heating CaCO3, if the system is closed and CO2 is not removed, the reaction will reach an equilibrium where the partial pressure of CO2 will prevent further decomposition. However, if CO2 is constantly removed from the system, the reaction will continue to proceed toward the production of CaO and CO2—this is commonly done in the manufacture of quicklime.
Therefore, at 850°C and with a CO2 partial pressure less than 1 atm, significant decomposition is expected, with the reaction potentially driven to completion if CO2 is removed as it is produced.