22.2 Enthalpy Changes in Solution

Question 1

What is enthalpy change of solution?

Answer 1

enthalpy change

1 mole of SOLUTE

DISSOLVED completely in WATER

under standard conditions

Question 2

1 mol Ionic lattice (s) ⟶ Cation (aq) + anion (aq)

Answer 2

enthalpy change of solution

Question 3

What events occur during dissolving an ionic lattice?

Answer 3

1. Polar H2O ATTRACTED to SURFACE of ionic lattice
   
   • H𝛅+ to anions, O𝛅- to cations
   • Electrostatic attraction between opposite ions decreases, WEAKENS ionic bonds.
2. Ionic bonds BREAK, forming gaseous ions.
3. Water molecules SURROUND ions, now aqueous.

Question 4

What is hydration enthalpy?

Answer 4

enthalpy change

1 MOL GASEOUS IONS

hydrated.

Question 5

What occurs during enthalpy of hydration?

Answer 5

formation of permanent dipoles

between gaseous ions + water molecules

forming aqueous ions

Question 6

How do you determine the enthalpy change of solution?

Answer 6

1. weigh sample of solid ionic lattice
2. measure volume + starting temperature of water.
3. add solid ionic compound into water + stir with thermometer until fully dissolved.
4. measure END TEMPERATURE.

Q = mcΔT to find energy change, then divide by number of moles + change sign.

Question 7

What are the units for Q in Q = mcΔT?

Answer 7

joules, J

Question 8

What are the units for m in Q = mcΔT?

Answer 8

kilograms, Kg

Question 9

What are the units for c in Q = mcΔT?

Answer 9

Joules per gram per degree Kelvin, J/gK

Question 10

What are the units for ΔT in Q = mcΔT?

Answer 10

does not matter since a change of 1 kelvin is equal to 1 degree celsius.

Question 11

What is Q = mcΔT used to calculate?

Answer 11

the change in heat energy. (usually of the surroundings)

Question 12

During enthalpy change of solution, energy is either absorbed or released by the ions of the _____ when _____ + becoming aqueous. This energy is either absorbed by or taken from the _____. so, calculating the temperature change of a mass of water, + the energy required to cause that temperature change calculates the overall energy change of the surroundings.

The increase in the energy of the surroundings = the energy _____ by the dissolving ionic lattice.

Answer 12

solid ionic lattice,

dissociating,

water,

released

Question 13

What changes of state occur during enthalpy change of solution?

Answer 13

solid ionic compound ⟶ gaseous ions ⟶ aqueous ions

Question 14

1 mol gaseous ions + aq ⟶ 1 mol aqueous ions

Answer 14

enthalpy of hydration

Question 15

What occurs during hydration of gaseous ions?

Answer 15

formation of INTERMOLECULAR forces (permanent dipole)

between GASEOUS IONS + WATER MOLECULES

(formation of intermolecular forces is exothermic)

Question 16

Solution enthalpy = _____ + _____

Answer 16

-LE + Hyd (of both cation & anion)

Question 17

Is solution enthalpy endothermic or exotherimic?

Answer 17

can be EITHER, depending on the relative magnitude of lattice enthalpy + hydration enthalpy.

sol = -LE + Hyd

Question 18

Why does solution enthalpy consist of -LE + Hyd?

Answer 18

Solid ionic lattice ⟶ gaseous ions
- LE

gaseous ions ⟶ aqueous ions
+ Hyd