Question

In general, the attractive intermolecular forces between solvent and solute particles must be comparable or greater than solute-solute interactions for significant solubility to occur. Explain this statement in terms of the overall energetics of solution formation.

Short answer

In summary, significant solubility occurs when the attractive intermolecular forces between solvent and solute particles (solute-solvent interactions) are comparable to or greater than the solute-solute and solvent-solvent interactions. This is because the overall energy change during solution formation (ΔH_solution) would be negative or close to zero, indicating that solubility is favored. Strong solute-solvent interactions compensate for the energy required to break the initial solute-solute and solvent-solvent interactions, thereby promoting solubility.

Step-by-step solution

Define solubility

Solubility is defined as the maximum amount of solute that can dissolve in a particular solvent at a specific temperature and pressure to form a homogeneous solution.

Understand intermolecular forces

Intermolecular forces are the forces between molecules that hold them together in a substance. These forces can be classified into three main types: dipole-dipole interactions, hydrogen bonding, and dispersion forces (London forces).

Describe the process of solution formation

The formation of a solution involves three steps: (1) breaking the solute-solute interactions, (2) breaking the solvent-solvent interactions, and (3) forming solute-solvent interactions. The overall energy change in this process determines whether a solution will form or not.

Explain the energetics of solution formation

The overall energy change in the formation of a solution can be represented by the equation: ΔH_solution = ΔH1 + ΔH2 + ΔH3, where ΔH1 is the energy required to break solute-solute interactions, ΔH2 is the energy required to break solvent-solvent interactions, and ΔH3 is the energy released when solute-solvent interactions are formed. In order for a solution to form, the overall energy change must be negative or close to zero, which means that the energy released from the formation of solute-solvent interactions must be equal to or greater than the energy required to break the initial solute-solute and solvent-solvent interactions.

Relate intermolecular forces and solubility

The statement in the exercise implies that when the attractive intermolecular forces between solvent and solute particles (solute-solvent interactions) are comparable to or greater than the solute-solute and solvent-solvent interactions, the overall energy change during solution formation (ΔH_solution) will be negative or close to zero, and significant solubility will occur. In other words, when the solute-solvent interactions are strong enough to compensate for breaking the initial solute-solute and solvent-solvent interactions, solubility will be favored.

Key concepts

Solubility

Solubility is a crucial concept in chemistry that refers to the ability of a solute to dissolve in a solvent. It's defined as the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature and pressure. This results in a homogeneous mixture known as a solution. Several factors influence solubility, including temperature, pressure, and the nature of the solute and solvent involved.

Understanding solubility is essential for predicting how substances will behave in a solution. When considering solubility, the intermolecular forces between solute and solvent particles play a key role. If the forces of attraction between the solute and solvent are strong enough, they can overcome the forces holding the solute particles together, leading to dissolution. Conversely, if the solute-solute forces are stronger, the substance may not dissolve readily.

Solution Formation

The process of solution formation involves a dynamic interaction of forces and an energy exchange. This process can be divided into three primary steps:

• Breaking solute-solute interactions: This step requires energy to overcome the forces holding the solute particles together, making them ready to disperse into the solvent.
• Breaking solvent-solvent interactions: Similarly, energy is needed to separate solvent molecules to provide room for the solute particles to mix.
• Forming solute-solvent interactions: This is an exothermic step where new interactions form between solute and solvent particles, releasing energy back into the system.

For a solution to form, the energy released during the formation of solute-solvent interactions should be comparable to or exceed that required to break initial solute-solute and solvent-solvent interactions.

Energetics of Solutions

The energetics underlying the solution formation is a balance of energy changes. The overall energy change (\(\Delta H_{solution} = \Delta H_1 + \Delta H_2 + \Delta H_3\) ) determines whether the solution process is favorable.

• \(\Delta H_1\) represents the energy needed to break solute-solute forces. This is usually an endothermic process.
• \(\Delta H_2\) accounts for the energy to separate solvent molecules from each other, which also generally consumes energy.
• \(\Delta H_3\) is the energy released when solute-solvent interactions form. This is an exothermic process that contributes to making the solution favorable.

For a solution to be energetically feasible, \(\Delta H_3\) should be greater than or equal to the total of \(\Delta H_1\) and \(\Delta H_2\) , resulting in \(\Delta H_{solution}\) being zero or negative. This means the energy gained from forming new solute-solvent interactions compensates for the energy invested in breaking the initial interactions. When this balance is maintained, solubility is likely to occur, facilitated by favorable intermolecular attractions.