12B - Energy, Heat and Disorder

Question 1

Theory: Consider Pure A with A-A interactions, and B with B-B interactions. What interactions will a soln of both have? What conditions will be favorable for solubility?

Answer 1

A-A, B-B, A-B

If A-B is similar to A-A or B-B are greater.

Question 2

Theory: Regarding solubility, ____ dissolves in ____.

Answer 2

Like

Question 3

Theory: What will ionic compounds be most soluble in?

Answer 3

Polar solvents.

Question 4

Theory: Describe the process of mixing solvent and solute, using enthalpies and heat.

Answer 4

1. Solvent breaks apart, breaking IF’s, in endothermic rxn, delta-H1
2. Solute breaks, breaking IF’s, apart in endothermic rxn, delta-H2
3. Solvent and solute combine, making new IF’s, in exothermic rxn, delta-H3.
   delta-H-soln = delta-H-solvent + delta-H-solute + delta-H-mixing
   or = delta-H1 + delta-H2 + delta-H3

Question 5

Theory: Using the formula for delta-H-soln, what result will mean it’s likely that dissolving occurs?

Answer 5

If it’s negative overall. The rxn should be exothermic.

Question 6

Theory: Why are some ionic compounds soluble, and why are some not?

Answer 6

Charge density and delta-H2
CD: q/SA
q is charge
- High surface charge density opposes solubility
_ Low CD means soluble

Question 7

Theory: What does delta-H3 compensate for?

Answer 7

Compensate for endothermic processes of delta-H1 and delta-H2.

Question 8

Theory: consider the following situations and determine if a solution will form.
H1 H2 H3 Hsoln
1. L,+ L,+ L, - S, +-
2. S,+ L,+ L, - L,+
3. S, + S, + S, - S, +-

Answer 8

If either H1 or H2 is large, h-soln will be large and +. If both are the same, h-soln will be small and +/-.
Soln will form
Soln will not form
Soln will form.

Question 9

Theory: In the case where Hsoln is a small positive, why can dissolution occur?

Answer 9

Entropy can compensate for it.

Question 10

Theory: What is a small heat of soln? What sign of heat of solution will aid solubility? If the sign will not aid solubility, how can it be compensated

Answer 10

abs(delta-hsoln) < 80 kj/mol
(-)
Compensated by increased entropy of soln

Question 11

Theory: What happens to ion-ion interactions of ionic compounds when dissolved?

Answer 11

Replace by ion-dipole.

Question 12

Def: what is a hydration shell? Why do they form? Relate the hydration and lattice energies in terms of dissolution.

Answer 12

Shell in which water molecules orient around the ions is solution. Form due to ion-dipole force present.
Hydration > Lattice E, more favorable dissolution

Question 13

Def: What is an electrolyte?

Answer 13

Soln formed from ionic species are conductors of electricity.

Question 14

Def: What is solvation? What is this process referred to when it occurs in water?

Answer 14

Process of sorrounding particle with solvent particles. Called hydration in water

Question 15

Theory: Is hydrtaion exo or endothermic? Why?

Answer 15

Always exothermic and negative. Due to ions in gas state being unfavorable, so being put in water which is favorable, releases energy.

Question 16

Theory: What contributes to a strong heat of hydration and high lattice energy? What is the periodic trend fro heat of hydration?

Answer 16

High charges and small ionic radius.

Decrease down group, increase across period.

Question 17

Def: What is the enthalpy of solution in terms of lattice and hydration energies

Answer 17

delta-Hsoln = deltaH-lattice + deltaH-hydration

Question 18

Theory: What happens to solute-solute attraction of molecules when dissolved? When can this occur?

Answer 18

Replaced by solute-solvent. Only occurs if the forces are similar.

Question 19

Def: What is entropy? Why is it important?

Answer 19

Entropy means disorder. Systems tend to favor configs that increase disorder. Disorder means homogeneity which is driving force in soln. Disorder minimses Ep by maximising attractive forces.

Question 20

Theory: Natural tends to favor _ and _.

Answer 20

Mixing, disorderr.