Question

When a bottle of soda water is opened, the partial pressure of \(\mathrm{CO}_{2}\). (a) decreases (b) increases (c) remains the same (d) none of these

Short answer

(a) decreases

Step-by-step solution

Understanding Change in Pressure

When a bottle of soda is closed, the carbon dioxide is pressurized. This means there is a high pressure inside the bottle because of the CO2 gas trapped inside.

Understanding the Effect of Opening the Bottle

On opening the bottle, the \(\mathrm{CO}_{2}\) is allowed to escape, thereby reducing the amount of \(\mathrm{CO}_{2}\) present inside the bottle.

Consequence on the Partial Pressure of CO2

Since the amount of \(\mathrm{CO}_{2}\) inside the bottle reduces when the bottle is opened, the partial pressure of the \(\mathrm{CO}_{2}\) inside the bottle decreases.

Key concepts

Partial Pressure

Unraveling the concept of partial pressure is key in understanding the behavior of gases when they are in mixtures. Each gas in a mixture exerts its own pressure, as if it were alone occupying the entire volume. This is known as the gas's partial pressure.

• When gases are mixed, their pressures add up to form the total pressure of the mixture.
• The partial pressure is proportional to the number of moles of the gas in the mixture.

In our example with a soda bottle, the carbon dioxide (\(\mathrm{CO}_{2}\)) has a specific partial pressure, contributing to the overall pressure inside the sealed bottle.
When the soda bottle is opened, the \(\mathrm{CO}_{2}\) begins to escape, leading to a decrease in its partial pressure. This is because there are fewer moles of \(\mathrm{CO}_{2}\) remaining, impacting how much pressure it can exert inside the bottle.

Carbon Dioxide

Carbon dioxide (\(\mathrm{CO}_{2}\)) is a colorless, odorless gas, naturally occurring as part of Earth's atmosphere. It plays a significant role in various processes, including respiration and photosynthesis.

• In beverages like soda, carbon dioxide is dissolved under pressure, creating carbonation.
• When pressurized CO2 is released, it returns to its gaseous state forming bubbles.

While the soda bottle is sealed, \(\mathrm{CO}_{2}\) remains dissolved due to high pressure. Once the bottle opens, the drop in pressure allows \(\mathrm{CO}_{2}\) to escape as gas bubbles, which is why the fizz and effervescence occur. This phenomenon is primarily responsible for the decrease in the beverage's carbon dioxide partial pressure.

Pressure Changes in Gases

Pressure changes are pivotal in determining how gases behave, especially when transitioning between high and low-pressure environments.
In a closed soda bottle, the pressure is higher because of the trapped gases, primarily carbon dioxide. Opening the bottle leads to a notable pressure change because:

• The gas inside releases, resulting in a balance with the atmospheric pressure outside.
• The sudden decrease in pressure reduces the solubility of the gas, causing it to escape.

This pressure change not only decreases the partial pressure of carbon dioxide but also the total pressure within the soda bottle. Understanding these gas laws helps us explain everyday experiences, like the fizz in your drink when you crack open a bottle of soda.