Enthalpy changes of solution and hydration

Question 1

one of the factors that determines solubility is the value of the

Answer 1

enthalpy change of solution

Question 2

the enthalpy change of solution is

Answer 2

the enthalpy change when one mole of an ionic solid dissolves in water to form an infinitely dilute solution
ΔsolH

Question 3

the equation that represents the enthalpy change of solution of sodium chloride is :

Answer 3

aq

NaCl(s) → Na+(aq) + Cl-(aq)

Question 4

upon dilution, the ions become further apart, which is a(n) …….thermic process

Answer 4

endothermic process

Question 5

upon dilution, ions become more hydrated, which is a(n) …….thermic process

Answer 5

exothermic process

Question 6

when further dilution has no measurable effect on ΔsolH, then this is the point of

Answer 6

point of infinite dilution

Question 7

the enthalpy change of hydration is

Answer 7

the enthalpy change when one mole of an ion in its gaseous state is completely hydrated by water

Question 8

when a solution has reached infinite dilution, …………………….is said to have occured

Answer 8

complete hydration has happened

Question 9

the equations which represent the enthalpy change of hydration for sodium chloride is

Answer 9

Na+(g) → Na+(aq)

Cl-(g) → Cl-(aq)

Question 10

water molecules are attracted to both positive and negative ions because they are

Answer 10

H2O is polar

Question 11

ion-dipole interactions are

Answer 11

the interactions that come as a result of the attraction between the δ- Oxygen atom in the water molecule and the cation, which has a positive charge

Question 12

for anions, such as chlorine, the ion-dipole interaction occurs because

Answer 12

the δ+ hydrogen atoms in the H2O molecules are attracted to the anion, and in chlorine’s case, form hydrogen bonds using the lone pairs of electrons on the chloride ion

Question 13

factors which affect the magnitude of the hydration enthalpy are

Answer 13

→the charge on the ion, as a Ca2+ has a much greater (more negative) ΔhydH than Na+ which has a single positive charge
→the ionic radius, with increasing radius, the energy released during hydration decreases, so the value is less negative because the electrostatic forces between the ions and the H2O molecules decreases
→the charge density also has an impact, with greater charge density of the cation resulting in a more negative value of ΔhydH

Question 14

use the various enthalpy changes involved in the dissolution of sodium chloride to show the relationship between ΔsolH, ΔhydH and ΔlatticeH

Answer 14

ΔlatticeH [NaCl(s)] + ΔsolH [NaCl(s)] = ΔhydH [Na+(g)] + ΔhydH [Cl-(g)]