Solid calcium carbonate (CaCO₃) decomposes into solid calcium oxide (CaO) and gaseous carbon dioxide (CO₂) in a constant-volume (100 cm³) 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 initial number of moles of CaCO₃, CaO, and CO₂ in the constant-volume container using sliders; the container displays the equilibrium pressure. The bar graph on the right shows the number of moles present at equilibrium. The equilibrium constant K_eq changes as the temperature changes using the slider. The equilibrium constant is equal to the CO₂ pressure (in bar) divided by the standard-state pressure of 1 bar. Note that adding more CaO when CaO is already in the container (or adding more CaCO₃ when CaCO₃ 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.

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 ref refers to a reference state, \( K_{eq} \) is the equilibrium constant, \( T \) is temperature (K), \( R \) is the ideal gas constant, \( \Delta H^\circ \) is the standard enthalpy of reaction (kJ/mol), and \( \Delta G^\circ \) is the standard Gibbs free energy of reaction (kJ/mol).

where \( P \) is the pressure (bar), \( n_i \) is the number of moles of component \( i \) initially in the system, \( n_{i(f)} \) is the final number of moles in the system, \( V \) is the fixed volume of the container (cm³), and \( \zeta \) is the extent of reaction.

This simulation was created in the Department of Chemical and Biological Engineering, at University of Colorado Boulder for LearnChemE.com by Pramod Kumar Ajmera under the direction of Professor John L. Falconer and Michelle Medlin, with the assistance of Neil Hendren. It is a JavaScript/HTML5 implementation based on a Mathematica simulation developed by Rachael L. Baumann and Garrison Vigil. It was prepared with financial support from the National Science Foundation (DUE 2336987 and 2336988) in collaboration with Washington State University. Address any questions or comments to LearnChemE@gmail.com.