The solubility of a gas in a liquid, such as carbon dioxide in water, depends on external conditions. How does its solubility change with pressure and temperature?

Introduction / Context:

The solubility of gases in liquids is important in many everyday situations, such as the carbonation of soft drinks, dissolved oxygen in water for aquatic life, and industrial absorption processes. This question examines the combined effect of pressure and temperature on gas solubility in a liquid.

Given Data / Assumptions:

• We consider a gas dissolved in a liquid, for example carbon dioxide in water.
• Pressure of the gas above the liquid can be varied.
• Temperature of the system can also be changed.
• We assume no chemical reaction is changing the gas into another species.

Concept / Approach:

Henry law states that at constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas above the liquid. Thus, higher pressure pushes more gas molecules into solution. Temperature has the opposite effect; as temperature rises, gas molecules gain kinetic energy and escape more easily from the liquid, reducing solubility. That is why warm soda loses its fizz quickly. Therefore, we must look for the option that combines increased solubility with increasing pressure and decreased solubility with increasing temperature.

Step-by-Step Solution:

Verification / Alternative check:

Think about a sealed cold drink bottle. It is filled under high pressure, which allows much more carbon dioxide to dissolve. When you open the bottle and release pressure, gas comes out as bubbles. Also, if the drink is warmed, it goes flat faster, showing that gas solubility is lower at higher temperature.

Why Other Options Are Wrong:

Option A: It increases with increasing pressure only mentions pressure and ignores the temperature effect, so it is incomplete.

Option B: It decreases with increasing temperature only mentions temperature and neglects the known effect of pressure.

Option D: It is independent of both pressure and temperature contradicts experimental evidence and basic gas solubility theory.

Common Pitfalls:

Students may remember only one factor, such as pressure, and forget temperature. Others might confuse gas solubility with the behaviour of solids, where solubility often increases with temperature. It is important to distinguish that for gases, higher temperature usually reduces solubility in liquids.

Final Answer:

The correct combined behaviour is that gas solubility increases with increasing pressure and decreases with increasing temperature.