Heterogeneous Chemical Equilibrium with Calcium Carbonate
Solid calcium carbonate () decomposes into solid calcium oxide () and gaseous carbon dioxide () in a constant-volume container at high temperatures. Carbon dioxide is assumed to be an ideal gas, and the two solids are assumed to be in separate phases. You can vary the number of moles of , , and added to the constant-volume container using sliders. The container displays the equilibrium pressure; the color intensity of the gas phase increases as the number of moles of increases. The bar graph on the right shows the number of moles present at equilibrium. The equilibrium constant changes as the temperature changes using the slider. The equilibrium constant is equal to the pressure (in bar) divided by the standard-state pressure of 1 bar. Note that adding more when is already in the container (or adding more when is already in the container) at equilibrium does not change equilibrium because increasing the number of moles of a pure solid does not change its fugacity.
Contributed by: Rachael L. Baumann and Garrison Vigil (February 2015)
Additional contributions by: John L. Falconer and Nick Bongiardina
(University of Colorado Boulder, Department of Chemical and Biological Engineering)
Open content licensed under CC BY-NC-SA
For this reaction, the equilibrium constant is equal to the equilibrium pressure (in bar) divided by 1 bar pressure. The equilibrium constant is calculated as a function of temperature using the Van't Hoff equation:
where the subscript refers to a reference state, is the equilibrium constant, is temperature (K), is the ideal gas constant, is the standard enthalpy of reaction (kJ/mol), and is the standard Gibbs free energy of reaction (kJ/mol).
where is the pressure (bar), is the number of moles of component initially in the system, is the final number of moles in the system, is the fixed volume of the container (), and is the extent of reaction.
The screencast video at  explains how to use this Demonstration.
 Heterogeneous Chemical Equilibrium with Calcium Carbonate. www.colorado.edu/learncheme/thermodynamics/HeterogeneousChemicalEquilibriumCaCO3.html.