Solutions: Solubility and Energy

Question 1

What is a solution?

Answer 1

A homogenous mixture

Question 2

What does the physical state of a solution usually depend on?

Answer 2

The physical state of the solvent

Question 3

When liquids form a solution, are they miscible or immiscible?

Answer 3

Miscible

Question 4

When liquids separate and don’t form a solution, are they miscible or immiscible?

Answer 4

Immiscible

Question 5

What does “like-dissolves-like” mean?

Answer 5

Substances with similar types of intermolecular forces dissolve in each other

Question 6

Polar and ionic substances are most soluble in what types of solvents?

Answer 6

Polar solvents

Question 7

Nonpolar substances are most soluble in what types of solvents?

Answer 7

Nonpolar solvents

Question 8

What does solubility depend on?

Answer 8

The strength of IMFs between the solute and solvent relative to the strength of IMFs within the pure substance

Question 9

What are the three steps in energy change in solution formation?

Answer 9

1) Solute particles separate (ΔH solute)
2) Solvent particles separate (ΔH solvent)
3) Solute and solvent particles mix (ΔH mixing)

Question 10

Is the separation of solute and solvent particles endothermic or exothermic?

Answer 10

Endothermic

Question 11

Is the mixing of solute and solvent particles endothermic or exothermic?

Answer 11

Exothermic

Question 12

What equation represents the enthalpy of a solution?

Answer 12

ΔH soln = ΔH solute + ΔH solvent + ΔH mixing

Question 13

In an exothermic solution process, does the energy needed to separate solute and solvent particles exceed the energy released when the particles mix?

Answer 13

No

Question 14

In an endothermic solution process, does the energy needed to separate solute and solvent particles exceed the energy released when the particles mix?

Answer 14

Yes

Question 15

Under what condition may the solute not dissolve very much?

Answer 15

If ΔH soln is very positive (if the solution process is very endothermic)

Question 16

What is solvation?

Answer 16

When solute particles are surrounded by solvent particles. In water, it’s hydration

Question 17

What equation represents the enthalpy of solvation?

Answer 17

ΔH solvation = ΔH solvent + ΔH mixing

Question 18

If two substances have different IMFs are they likely to dissolve in each other?

Answer 18

No

Question 19

What is ΔH hydration?

Answer 19

The enthalpy change of separating water molecules and mixing solute particles with them

Question 20

Is hydration of an ion endothermic or exothermic? Why?

Answer 20

Exothermic because water’s H-bonds are broken (endothermic) and replaced with stronger ion-dipole forces (more exothermic)

Question 21

Entropy is related to what quality?

Answer 21

Disorder

Question 22

Which physical state has the highest entropy?

Answer 22

Gas

Question 23

Which has higher entropy, a solution or the pure solute and solvent?

Answer 23

The solution

Question 24

Systems change toward
1) higher or lower enthalpy?
2) higher or lower entropy?

Answer 24

Lower ethalpy, higher entropy

Question 25

What is charge density?

Answer 25

An ion's ratio of charge to volume

Question 26

Does increasing an ion's charge and decreasing its volume raise or lower its charge density?

Answer 26

Raises charge density

Question 27

As charge density increases, does ΔH hydration increase or decrease?

Answer 27

Decreases

Question 28

As charge density decreases, does ΔH hydration increase or decrease?

Answer 28

Increases