Question

How does keeping a carbonated beverage capped help keep it from going "flat"?

Answer 1

The beverages which have dissolved carbon dioxide are known as carbonated drinks. The process of dissolving carbon dioxide in a liquid is known as carbonation. The fizz in the carbonated beverages is due to the dissolved carbon dioxide in the liquid. Carbonated drinks are prepared by mixing carbonated water with flavored syrups.

Complete answer: Now, we know that carbonated drinks are formed by the process of carbonation. The process of carbonation is essentially making a solution of gas dissolved in water.
The dissolution of a gas in a liquid is governed by Henry's Gas Law.
Henry's gas law states that the amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid.
So, according to Henry's law, the amount of carbon dioxide gas $C{{O}_{2}}$ dissolved in water is directly proportional to the partial pressure of the gas above the solution.
${{P}_{C{{O}_{2}}}}={{K}_{B}}{{C}_{C{{O}_{2}}}}$
Here, the partial pressure of $C{{O}_{2}}$ is denoted by ${{P}_{C{{O}_{2}}}}$, Henry's law constant is denoted by ${{K}_{B}}$, and the concentration of $C{{O}_{2}}$ gas at equilibrium is denoted by ${{C}_{C{{O}_{2}}}}$.
This concept is used in the process of making and packaging of carbonated beverages. Carbonated drinks are packed under so much pressure that all the carbon dioxide gas dissolves in the liquid.
Before we open the drink, the container is almost full of pure $C{{O}_{2}}$ gas. When the bottle is opened, and the pressure is removed or decreases, the solution becomes effervescent.
This is because upon opening the bottle, the equilibrium inside the bottle is disturbed and the solubility decreases as the partial pressure decreases. The $C{{O}_{2}}$ gas escapes the liquid in the form of small bubbles, and after all the dissolved $C{{O}_{2}}$ gas elopes, and the liquid is degassed, the beverage falls "flat".

Note: It should be noted that the dissolution of gas in a liquid also depends on the temperature. Henry's law constant ${{K}_{B}}$ increases when there is an increase in temperature. And hence with the increase in temperature, the solubility of the gas in a liquid decreases.