Problem 13 - Chemistry The Central Science In Si Units

Question

Indicate whether each statement is true or false: (a) A solute will dissolve in a solvent if solute-solute interactions are stronger than solute-solvent interactions. (b) In making a solution, the enthalpy of mixing is always a positive number. (c) An increase in entropy favors mixing.

Step-by-Step Solution

Answer

(a) False, (b) False, (c) True.

Step 1: Understanding Solute and Solvent Interactions

Statement (a) states that a solute will dissolve in a solvent if solute-solute interactions are stronger than solute-solvent interactions. In reality, dissolution occurs more readily when solute-solvent interactions are strong, allowing the solute particles to disperse into the solvent. Therefore, when solute-solvent interactions are stronger, not solute-solute, the solute is more likely to dissolve. Thus, this statement is False.

Step 2: Examining Enthalpy of Mixing

Statement (b) claims that the enthalpy of mixing is always a positive number. The enthalpy of mixing could be either positive or negative depending on the balance of energy absorbed or released during the dissolution. If more energy is required to break solute-solute and solvent-solvent bonds compared to the energy released upon forming solute-solvent bonds, the enthalpy will be positive, otherwise it will be negative. Thus, this statement is False.

Step 3: Analyzing Entropy's Influence on Mixing

Statement (c) explores the role of entropy in mixing. Entropy reflects the degree of disorder or randomness in a system. An increase in entropy typically favors spontaneous processes, including mixing, because systems tend to move towards higher disorder. Therefore, an increase in entropy does favor mixing. Hence, this statement is True.

Key Concepts

Solute-Solvent Interactions

In solution chemistry, understanding how solutes and solvents interact is vital. When a solute dissolves in a solvent, the solute-solvent interactions come into play in a big way. Generally, solute particles are surrounded by solvent molecules, which allows them to disperse uniformly throughout the solvent. This dispersion is possible because the solute and solvent molecules attract each other.

• For a successful dissolution, solute-solvent interactions need to be stronger than solute-solute interactions.
• This attraction helps overcome the forces holding the solute particles together, allowing them to become immersed in the solvent.

When solute-solute interactions are stronger, solute particles prefer to remain bonded to each other, which makes mixing much more difficult. Thus, strong solute-solvent interactions are key to the solubility of a substance.

Enthalpy of Mixing

The enthalpy of mixing is a concept from thermodynamics that helps explain energy changes during dissolution. It represents the heat absorbed or released when solute and solvent combine. The enthalpy of mixing can be either positive or negative:

• If the energy required to separate solute and solvent molecules is greater than the energy released when they create new bonds, the enthalpy is positive, suggesting that the reaction is endothermic.
• Conversely, if less energy is needed to disrupt the original interactions than is released during forming new interactions, the enthalpy is negative, indicating an exothermic process.

Thus, the enthalpy of mixing isn't always positive; it is entirely dependent on the specific interaction dynamics between the solute and solvent.

Entropy and Mixing

Entropy reflects the level of disorder in a system, and it plays a crucial role in the mixing process. It is a measure of how much energy in a system is unavailable to do work, often described as a system's tendency towards chaos.

• A higher entropy state is more probable because nature tends to favor disorder and randomness over order.
• Thus, an increase in entropy generally encourages the mixing of substances.

This is because mixing increases the number of possible configurations for the dissolved particles, leading to a higher entropy state. Therefore, in most cases, an increase in entropy favors the mixing process, making it a driving force for spontaneous dissolution.