Problem 74 - Introductory Chemistry Atoms First

Question

When a gaseous solute dissolves in water, which step in the dissolving process is essentially skipped? Explain why.

Step-by-Step Solution

Answer

When a gaseous solute dissolves in water, the step that is essentially skipped is the breaking apart of solute particles (Step 1). The reason for this is that gaseous solutes are already in the form of individual particles (molecules or atoms) before they dissolve in water, with weak attractive forces between them. Thus, when the gaseous solute comes into contact with water, the solvation process occurs directly, without the need to overcome strong intermolecular forces between solute particles.

Step 1: Understand the dissolving process

To answer this question, we first need to know the general steps involved in the dissolving process. The dissolving process involves three main steps: 1. Breaking apart solute particles (ex: ions or molecules) 2. Breaking apart solvent particles (ex: water molecules) 3. Solvent particles surround the solute particles, which is known as solvation.

Step 2: Determine the skipped step for gaseous solutes

In the case of a gaseous solute dissolving in water, one step that is essentially skipped is the breaking apart of solute particles (Step 1).

Step 3: Explain why the step is skipped

The reason for skipping the breaking apart of solute particles is that gaseous solutes are already in the form of individual particles (molecules or atoms) before they dissolve in the water. Gaseous solutes are far apart from each other, and the attractive forces between them are much weaker than those in solid or liquid solutes. When the gaseous solute comes in contact with the water, solvent particles (water molecules) immediately surround it, without needing to break apart the solute particles. This process is called solvation, which occurs directly without the need to overcome strong intermolecular forces between the solute particles.

Key Concepts

Dissolving Process

The dissolving process is a fascinating procedure where a solute becomes integrated into a solvent. It typically unfolds in three essential steps: breaking apart the solute particles, breaking apart the solvent particles, and then solvation.

• Breaking Apart Solute Particles: This is often necessary for solid and liquid solutes, where the particles are tightly bonded. It requires energy to separate these particles in order to mix them into the solvent.
• Breaking Apart Solvent Particles: The solvent, often water, must also have its particles separated to some degree. This makes space for the solute particles.
• Solvation: This is the final step where the solute particles become surrounded by solvent particles.

For gaseous solutes, the dissolving process is slightly different. Because gas particles are already widely spaced and less strongly bonded, the step of breaking apart solute particles is often skipped. This allows for a more direct interaction with the solvent, making the process efficient and unique for gases.

Solvation

Solvation is the stage in the dissolving process where the solvent surrounds the solute particles. This interaction is critical for dissolving to occur, as it stabilizes the solute within the solvent.

• How It Works: During solvation, the solvent particles encircle the solute particles. This can involve hydrogen bonding, dipole-dipole interactions, or van der Waals forces, depending on the nature of both the solute and solvent.
• Importance in Solution Formation: Solvation reduces the energy and stabilizes the solute in the solvent, making the solution homogeneous.
• Solvation with Gases: With gaseous solutes, solvation happens swiftly as they do not require the dissociation step that solids or liquids do.

Gaseous solutes skip the initial stages because their particles are already individual molecules or atoms, promoting rapid solvation due to weak intermolecular forces. This difference highlights the efficiency of solvation with gases.

Solute Particles

Solute particles can vary greatly depending on their state before dissolution. Understanding these particles and their behavior is key to grasping the dissolving process.

• Solids and Liquids: In these states, solute particles have strong intermolecular forces holding them together. Dissolution requires these forces to be overcome, which is why breaking apart solute particles is necessary.
• Gaseous Solute Particles: Unlike solids or liquids, gases consist of particles in a dispersed and energetic state. They do not need to be separated from each other to dissolve in a solvent.
• Unique Behavior in Solution: Since gases do not need to be broken apart, they can dissolve into a solvent more readily than solids or liquids. This readiness is due to their pre-existing dispersed state and weak particle interactions.

Recognizing the nature of solute particles in each state helps to appreciate why gaseous solutes skip the initial breaking apart step in the dissolving process. It emphasizes the inherent differences and efficiencies in dissolving different types of solutes.