Carbonic acid (H₂CO₃) is formed when carbon dioxide (CO₂) dissolves in water (H₂O).
This process is a reversible reaction, meaning it can proceed in both directions. While seemingly simple, the reaction involves several steps and exists in equilibrium. Here's a breakdown:
- Dissolution: Carbon dioxide molecules dissolve in water.
- Hydration: The dissolved carbon dioxide reacts with water molecules to form carbonic acid.
The reaction is represented by the following equation:
CO₂ (aq) + H₂O (l) ⇌ H₂CO₃ (aq)
Where:
- CO₂ (aq) represents dissolved carbon dioxide
- H₂O (l) represents liquid water
- H₂CO₃ (aq) represents carbonic acid
It's important to note that the equilibrium strongly favors the reactants, meaning that at any given time, only a small fraction of the dissolved carbon dioxide is converted into carbonic acid. Most of the carbon dioxide remains as dissolved CO₂. Also, carbonic acid readily decomposes back into carbon dioxide and water.
The presence of carbonic acid influences the pH of the water, making it slightly acidic. This is particularly important in natural water systems like oceans and lakes, where the dissolved carbon dioxide contributes to the overall acidity and plays a role in buffering pH changes.
