Question

Why do carbonated beverages go "flat" after being opened for some time?

Short answer

Carbonated beverages go 'flat' after being opened because the decrease in container pressure allows the dissolved carbon dioxide gas to escape from the liquid and into the air. Over time, this loss of carbon dioxide results in the drink losing its bubbliness and going 'flat'.

Step-by-step solution

Understanding the carbonation process

Carbonated drinks contain dissolved carbon dioxide gas. The carbon dioxide is dissolved into the drink under high pressure during the manufacturing process. The pressure inside a closed bottle or can is higher than the atmospheric pressure outside of it, and this high pressure helps to keep the carbon dioxide gas dissolved in the liquid.

The role of opening a beverage

When a carbonated drink is opened, the pressure inside the container decreases to become the same as the atmospheric pressure outside. This decrease in pressure means that there's now less force keeping the carbon dioxide gas dissolved in the liquid. As a result, the carbon dioxide begins to come out of solution, forming bubbles.

Going 'flat'

If a carbonated drink is left open for some time, most of the dissolved carbon dioxide gas will escape from the liquid and into the air. This is because there's no longer enough pressure to keep it dissolved. As less and less carbon dioxide gas remains dissolved in the drink, it loses its bubbliness and goes 'flat'.

Key concepts

Dissolved Carbon Dioxide

Carbon dioxide (CO2) is a colorless and odorless gas that is a byproduct of respiration, combustion, and organic decomposition. It is also a crucial component in the carbonation process of beverages. When CO2 is dissolved in water, it forms carbonic acid, giving carbonated drinks their characteristic tanginess and bite. The solubility of CO2 in a liquid beverage is determined by factors such as temperature and pressure. Under high-pressure conditions, like in sealed cans and bottles, more CO2 can dissolve into the drink, thus making it fizzy and effervescent.

• CO2 creates fizz and tanginess by forming carbonic acid.
• High pressure allows for more CO2 to dissolve in liquids.

Pressure and Gas Solubility

The relationship between pressure and the solubility of gases in liquids is described by Henry's Law. This principle states that at a constant temperature, the amount of gas that dissolves in a liquid is directly proportional to the partial pressure of that gas above the liquid. This is why carbonated beverages are pressurized during manufacturing to dissolve more CO2. Once the pressure is released, as when a beverage is opened, the solubility of CO2 decreases, and the excess gas escapes, forming bubbles.
Some key points include:

• Henry's Law explains how gas solubility and pressure are related.
• Greater the pressure, the more gas can be dissolved.
• Opening the beverage releases pressure and decreases CO2 solubility.

Loss of Carbonation

The loss of carbonation is a phenomenon that occurs when the dissolved CO2 in a carbonated beverage escapes into the atmosphere, leading to a 'flat' drink. When the pressure in a beverage container is reduced by opening it, CO2 starts to escape because the conditions that kept it dissolved (high pressure) are no longer present. Over time, and especially if the beverage is left open, the remaining CO2 will continue to leave the solution, until the pressure of CO2 above the liquid is equivalent to atmospheric levels, leaving the drink with little to no fizz.

• Reduction in the container's pressure allows CO2 to escape as gas.
• Drinks go 'flat' when exposed to atmospheric pressure for extended periods.
• Re-sealing the container helps slow the loss of carbonation by maintaining pressure.