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.

Short answer

(a) False - A solute will dissolve in a solvent if the solute-solute interactions are weaker than the solute-solvent interactions. (b) False - The enthalpy of mixing can be both positive or negative, depending on whether the mixing is endothermic or exothermic. (c) True - An increase in entropy favors mixing, as it increases the disorder of the solute and solvent molecules.

Step-by-step solution

(a) Solute-solute vs solute-solvent interactions

A solute will dissolve in a solvent if the solute-solute interactions are weaker than the solute-solvent interactions. This is because, for a solute to dissolve in a solvent, it needs to create new interactions with the solvent, which will be stronger and more favorable than the original solute-solute interactions. Therefore, this statement is false.

(b) Enthalpy of mixing

The enthalpy of mixing refers to the amount of energy (heat) that is either absorbed or generated due to the mixing of two substances. The enthalpy of mixing can be a positive or a negative number, depending on whether the mixing is endothermic (energy is absorbed, a positive number) or exothermic (energy is released, a negative number). Therefore, this statement is false.

(c) Increase in entropy and mixing

Entropy is a measure of the degree of disorder in a system. Higher entropy indicates more randomness, while lower entropy indicates a more ordered state. An increase in entropy generally favors mixing because mixing increases the disorder of the solute and the solvent molecules. Thus, this statement is true.