Ocean Acidification

As atmospheric levels of carbon dioxide rise due to human activity, oceans are becoming more acidic. This ocean acidification can be understood by using our knowledge of chemical equilibrium systems.

Consider the following equilibria that exist in our oceans...

Using our knowledge of Le Châtelier’s Principle and collision theory, we know that an increase in the partial pressure (or concentration) of atmospheric carbon dioxide will cause the physical equilibrium [1] to shift to the right, leading to an increase in the concentration of aqueous carbon dioxide.

Using the same principles, this increase in the concentration of aqueous carbon dioxide will shift equilibrium [2] to the right, increasing the concentration of carbonic acid.

Similarly, the increase in the concentration of carbonic acid will shift equilibrium [3] to the right, increasing the concentration of hydrogen carbonate anions and hydronium cations. The increase in the concentration of hydronium resulting from this shift will be relatively larger than the increase in hydrogen carbonate (the initial concentration of hydrogen carbonate in the ocean is greater than the initial concentration of hydronium).

The increased concentration of hydronium ions will contribute to an increase in the acidity of our oceans.

Additionally, because the relative increase in the concentration of hydronium is greater than the relative increase in the concentration of hydrogen carbonate, equilibrium [4] will shift to the left. As a result of this shift, there will be a decrease in the concentration of carbonate ions, causing equilibrium [5] to shift to the right and dissolving solid calcium carbonate in the process. Consequently, calcifying marine organisms (coral, lobster, starfish, osysters, etc...) will find it increasingly difficult to form their exoskeletons.

The Kyoto Protocol

The Kyoto Protocol was a UN treaty which aimed to reduce global greehouse gas emissions (including CO2) in order to mitigate the impact of human-driven climate change. Since its signing in 1997, there have been many other international conferences and agreements that address similar concerns to the Kyoto Protocol (notably the 2015 Paris Agreement and the 2021 Glasgow Climate Pact), indicating the importance of addressing greehouse gas emissions on a global scale.

Climate agreements such as the Kyoto Protocol are relevant for the Year 12 Chemistry course because we, as chemists, can look to equilibrium equations (such as the ones on this page!) and see exactly how emissions of greenhouse gases affect our environment.