Question

How does temperature affect the solubility of \(\mathrm{O}_{2}\) in water? Explain what is meant by thermal pollution.

Short answer

Increased temperature decreases  solubility in water. Thermal pollution is when warm water discharge reduces dissolved  levels, affecting aquatic life.

Step-by-step solution

Understanding Solubility

Solubility is the ability of a gas or solid to dissolve in a liquid. In this case, we are examining how much oxygen () can dissolve in water.

Temperature Effect on Solubility

As temperature increases, the kinetic energy of water molecules also increases. This increased motion tends to expel dissolved gases from the water into the atmosphere, reducing their solubility.

Application to  Solubility

For oxygen, higher water temperatures mean less oxygen can be dissolved. Colder water can hold more oxygen because the molecules are moving less, allowing more oxygen to remain dissolved.

Definition of Thermal Pollution

Thermal pollution occurs when industrial processes release hot water or wastewater back into natural water bodies, raising the water temperature and reducing dissolved oxygen levels, which can harm aquatic life.

Key concepts

Temperature Effect on Solubility

The solubility of gases in water is closely related to temperature. As temperature rises, water molecules gain kinetic energy, causing them to move and vibrate more vigorously. This increase in motion has significant implications for the solubility of gases like oxygen (\(\mathrm{O}_{2} \)). When water is heated, the ability of the liquid to "hold onto" dissolved gases diminishes. Water molecules that are more energetic make it easier for dissolved gases to escape back into the atmosphere. Therefore, at higher temperatures, less gas is able to remain dissolved. Conversely, when water is cold, the kinetic energy of the molecules is reduced, allowing more gas molecules to stay dissolved in the water. This means that cooler water can dissolve more oxygen compared to warmer water. A practical consequence of this relationship is observed in aquatic environments, where colder streams and lakes can support more aquatic life due to higher available oxygen levels.

Thermal Pollution

Thermal pollution is a particular environmental issue that arises primarily from industrial activities, such as power plants, that use water as a cooling agent. These facilities discharge warm or hot water back into rivers, lakes, or oceans, raising the natural water temperature significantly. This artificial warming of water bodies has several deleterious effects on the ecosystem:

• Reduced Oxygen Levels: As discussed, warmer water can hold less dissolved oxygen, essential for fish and other aquatic organisms.
• Thermal Shock: Sudden changes in temperature can lead to thermal shock for aquatic life, which may cause stress or even mortality.
• Altered Ecosystems: Certain species may thrive with increased temperatures, but this can upset the balance of the existing ecosystem, leading to biodiversity loss.

Therefore, managing thermal pollution involves regulating industrial discharges and implementing cooling techniques to minimize temperature changes in natural water bodies, protecting aquatic ecosystems.

Dissolved Oxygen in Water

Dissolved oxygen (DO) refers to the oxygen that is freely available in water to support aquatic life and is crucial for the survival of fish, invertebrates, and other marine organisms. Oxygen enters the water through a variety of natural processes, such as atmospheric diffusion, photosynthesis by aquatic plants, and surface agitation. Factors Affecting Dissolved Oxygen Levels:

• Temperature: As covered, temperature plays a vital role in the solubility of oxygen. Cooler waters naturally have higher DO levels.
• Salinity: The salt content in water can influence DO levels, with freshwater generally able to dissolve more oxygen than saltwater.
• Water Movement: Streams with higher flow rates usually aerate more, increasing oxygen levels.

Maintaining adequate levels of dissolved oxygen is critical for fish and other aquatic organisms, ensuring healthy aquatic ecosystems. Low levels of dissolved oxygen can lead to "dead zones" where marine life cannot survive. Thus, it is important to monitor and protect the delicate balance of oxygen levels in aquatic environments.