Heterogeneous Chemical Equilibrium with Calcium Carbonate

temperature (K)

1364

add moles of products and reactant to the system:

CaCO

3

1

CaO

1

CO

2

1

(s)

CaCO

3

←⟶

(s)

CaO

+

(g)

CO

2

Solid calcium carbonate (

CaCO

3

) decomposes into solid calcium oxide (

CaO

) and gaseous carbon dioxide (

CO

2

) in a constant-volume container at high temperatures. The equilibrium constant

K

eq

depends on temperature, which you can vary, and is equal to the

CO

2

pressure (in bars) divided by the standard-state pressure of 1 bar. Carbon dioxide is assumed to behave like an ideal gas, and the two solids are assumed to be in separate phases.

You can vary the number of moles of

CaCO

3

,

CaO

, and

CO

2

added to the constant-volume container; the bar graph on the right shows the number of moles present at equilibrium. Note that adding

CaO

(or

CaCO

3

when CaO (or

CaCO

3

) is already in the container at equilibrium does not change equilibrium because the fugacity of the solid does not change. The container on the left represents the system; the color of the gas phase increases in intensity as the number of moles of

CO

2

increases.