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Solubility of Carbon Dioxide, explained in terms of Le Chatelier’s Principle

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2.2.5 Describe the solubility of carbon dioxide in water under various conditions as an equilibrium process and explain in terms of Le Chatelier’s principle

This dotpoint is really just an application of Le Chatelier’s principle using the solubility of carbon dioxide as an example. As such, set yourself in the habit for such questions by starting with the equation, and then working through changes in concentration, pressure, volume and temperature.

Note that when you have soft drink in a glass or open bottle, you can see bubbles rising in it. This is because the carbon dioxide gas is constantly escaping, thereby constantly favouring the backwards reaction in an attempt to minimise the disturbance to the system. In comparison, a closed bottle of soft drink has no bubbles unless you shake it, because it is in equilibrium.

CO2 (g) + H2O(l) −↽−⇀− H2CO3 (aq) + Heat
Using the above equilibrium as a practical example of Le Chatelier’s principle:

  • An increase in the concentration of CO2 (g) will shift the equilibrium to the right, converting carbon dioxide and water into carbonic acid in order to reduce the concentration of carbon dioxide.
  • An increase in pressure will shift the equilibrium to the right, converting carbon dioxide and water into carbonic acid in order to reduce the pressure.
  • An increase in the volume of CO2 (g) will shift the equilibrium to the right, converting carbon dioxide and water into carbonic acid in order to reduce the volume of carbon dioxide. Thus the system will attempt to counteract this change by favouring the backwards reaction.
  • An increase in temperature will shift the equilibrium to the left, converting carbonic acid into carbon dioxide and water in order to reduce the temperature.
  • An increase in temperature will shift the equilibrium to the left, converting carbonic acid into carbon dioxide and water in order to reduce the temperature.

Remember- Le Chatelier’s principle will ensure that equilibrium is reached once again. However, this new point of equilibrium will not be same as the original point of equilibrium, as the impact was only minimised, not completely reversed. This is the reason why opened soft drinks will go ‘flat’ irreversibly. 

From The Student’s Guide to HSC Chemistry.