When a carbonated soft drink is stored in a closed container, it maintains a high pressure. This high pressure keeps the carbon dioxide (\(CO_2\)) dissolved in the liquid, favoring the formation of carbonic acid (\(H_2CO_3\)), as per the equilibrium reaction:
[tex]\[ H_2CO_3 \rightleftharpoons CO_2 + H_2O \][/tex]
Here is a detailed explanation step-by-step about what happens when the container is left open:
1. Pressure Change:
- Inside a closed container, the pressure is relatively high, maintaining a significant amount of dissolved \(CO_2\) in the drink.
- When the container is opened, the internal pressure of the container decreases and equalizes with the atmospheric pressure.
2. Effect on Equilibrium:
- According to Le Chatelier's Principle, reducing the pressure shifts the equilibrium position to favor the formation of more \(CO_2\) gas and less \(H_2CO_3\).
- As the pressure decreases, \(H_2CO_3\) decomposes to release \(CO_2\) and \(H_2O\) as a response to the lower pressure.
3. Carbon Addition and Escape:
- The decreased pressure means that \(CO_2\) gas is no longer held in the solution.
- This causes \(CO_2\) to escape from the liquid into the air.
- Escaping \(CO_2\) results in the loss of carbonation (the fizz).
4. Final Result:
- As more \(CO_2\) escapes, less \(H_2CO_3\) can be formed, and the drink becomes flat because of the loss of \(CO_2\) gas which forms the bubbles.
Therefore, the primary reason why a carbonated soft drink loses its carbonation when the container is left open is due to the decrease in pressure, which favors the formation of [tex]\(H_2CO_3\)[/tex]. This decrease in pressure drives the reaction to release [tex]\(CO_2\)[/tex] gas from the liquid, leading to the loss of carbonation.
