Question

Use Le Chatelier's principle to explain why the solubility of \(\mathrm{O}_{2}\) in water increases when the partial pressure of \(\mathrm{O}_{2}\) gas above the solution is increased.

Short answer

According to Le Chatelier's Principle, if the partial pressure of \(\mathrm{O}_{2}\) gas above the solution increases, the system shifts its equilibrium to reduce this change. The reaction moves towards the side with lower pressure, which is the aqueous phase (\(\mathrm{O}_{2_{(aq)}}\)). Therefore, more \(\mathrm{O}_{2}\) gas gets dissolved in water, increasing its solubility.

Step-by-step solution

Understanding of Le Chatelier's Principle

To start, it's key to have a sound understanding of Le Chatelier's Principle. It states if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change. In simpler terms, if you impose a change, the system will respond to reduce that change.

Consider the Reaction at Equilibrium

In the case of oxygen dissolving in water, the equilibrium can be represented by the following equation: \[ O_{2(gas)} \longleftrightarrow O_{2(aq)} \]The left-hand side of the equation represents oxygen in the gaseous phase, while the right-hand side represents oxygen dissolved in water (aqueous phase). This reaction is at equilibrium when the rate of dissolving of oxygen into water equals the rate of escaping of oxygen from the water.

Applying Le Chatelier's Principle

Now, if the partial pressure of \(O_{2(gas)}\) above the solution is increased, this means the concentration of \(O_{2(gas)}\) is increased. According to Le Chatelier's Principle, the system will respond by moving in the direction that decreases the concentration of \(O_{2(gas)}\), which in this case is to the right towards the \(O_{2(aq)}\). This means more \(O_{2(gas)}\) will get dissolved in water, increasing the solubility of \(O_{2}\).

Key concepts

Solubility

Solubility is a measure of how much of a substance (solute) can dissolve in a solvent to form a stable solution. Solubility can be affected by several factors, including temperature, pressure, and the nature of the solute and solvent. In the context of gases dissolving in liquids, such as oxygen in water, pressure plays a significant role.

When you increase the partial pressure of a gas above a liquid, more of that gas will dissolve in the liquid. This happens because the increased pressure exerts more force on the gas molecules, pushing them into the liquid where they find equilibrium. In this case, when the partial pressure of oxygen gas is increased, more oxygen molecules are pushed into the water, enhancing its solubility.

This concept is directly connected to Le Chatelier's Principle. Increasing the partial pressure disturbs the equilibrium, causing the system to shift and more oxygen to dissolve in water as it seeks to minimize the change imposed by the higher pressure.

Equilibrium

In a chemical context, equilibrium refers to the stage in a reversible reaction where the rates of the forward and backward reactions are equal. At equilibrium, the concentration of reactants and products remain stable over time, as long as the system is not disturbed. For oxygen dissolving in water, equilibrium is achieved when the rate of oxygen entering the water equals the rate of oxygen leaving it.

When a system at equilibrium experiences a change in conditions, Le Chatelier's Principle suggests that the system will react to partially counteract that change. This means altering the balance established at equilibrium. Increasing the partial pressure of oxygen gas encourages a shift in the equilibrium toward dissolving more gas in the liquid, thereby boosting the solubility of the gas in the water.

• An equilibrium shift often results in higher or lower concentrations of products and reactants.
• The direction of the shift depends on the change applied to the system (e.g., pressure, temperature).

Understanding equilibrium helps predict how different factors affect the balance in chemical reactions and the tendency to attain a new state of equilibrium under changed conditions.

Partial Pressure

Partial pressure is the pressure exerted by an individual gas component in a mixture of gases. It contributes to the total pressure exerted by the entire gas mixture. The concept of partial pressure is crucial in understanding how gases behave, particularly in dynamic equilibrium situations where gases interact with liquids.

For example, consider a closed container with water and oxygen gas. The partial pressure of oxygen is the pressure attributed to the oxygen molecules in the gaseous phase above the water. Increasing the partial pressure effectively means increasing the number of oxygen molecules per volume unit in the gas phase.

• Partial pressure impacts how much gas will dissolve in a solution, influencing solubility.
• Increasing partial pressure can lead more gas to dissolve, as the equilibrium will shift to accommodate this change, moving towards dissolving more gas.

Understanding partial pressure is integral to applications like calculating the solubility of gases in liquids and predicting the behavior of gases in chemical and physical processes.