Chemistry - The Molecular Science, Chap. 15

Front 1

Miscible

Back 1

Liquids that dissolve (mix) in each other

Front 2

Like dissolves ____

Back 2

Like dissolves _like_

Front 3

Solubility

Back 3

Maximum amount of solute that can dissolve in a solvent at a specified temperature

Front 4

"Methods" of predicting solubility

Back 4

1. substances with similar non-covalent forces are likely to be soluble in each other
2. Solutes do not readily dissolve in solvents whose noncovalent forces are quite different from their own
3. stronger solute-solvent attractions favor solubility. Stronger solute-solute or solvent-solvent attractions reduce solubility

Front 5

Enthalpy

Back 5

Heat/Energy Transfer

Front 6

ΔH

Back 6

change in the internal energy of the system, plus the work that the system has done on its surroundings

Front 7

Enthalpy of Solution ( ΔHsoln ) - definition

Back 7

Enthalpy of solution describes the net change in heat when a solute is dissolved in a solvent. Specifically, the standard enthalpy of solution is the heat change when one mole of solute is completely dissolved in a solvent to form a solution concentration of 1 mol per L under standard conditions.

The net change in heat can be broken down into the sum of two heats. First, the solute crystals must break from their lattice. This is known as the lattice enthalpy and its reversal is typically endothermic. Second, the ions are solvated (or hydrated in the case of aqueous solutions), which is typically an exothermic step. Depending on the magnitude of each of these factors, the sum can lead to a positive or negative enthalpy of solution.

Front 8

Enthalpy of Solution - formula

Back 8

ΔHsoln = ΔHstepa + ΔHstep b + ΔHstep c

Front 9

Saturated Solution

Back 9

Solution whose solute concentration equals its solubility

Front 10

Kc

Back 10

Concentration of solute (in solution)

Front 11

In a saturated solution at equilibrium, Q . . .

Back 11

saturated solution: Q = _Kc_

Front 12

Unsaturated solution

Back 12

Solution in which the concentration of solute is less than its solubility

Front 13

In a unsaturated solution at equilibrium, Q . . .

Back 13

unsaturated solution: Q < _Kc_

Front 14

In a supersaturated solution at equilibrium, Q . . .

Back 14

supersaturated solution: Q > _Kc_

Front 15

Lattice Energy

Back 15

Energy released when ions in a gaseous state form a crystal lattice solid

Front 16

Enthalpy of Hydration

Back 16

Energy released when new attractions form between ions and water molecules as they mix

Front 17

Enthalpy of Solution ( ΔHsoln ) - formula

Back 17

ΔHsoln = -(lattice energy) + ΔHhydration(cations) + ΔHhydration(anions)

Front 18

Thermodynamic state variable depends only on . . .

Back 18

. . . initial and final values

Front 19

Henry's Law - definition

Back 19

The solubility of any gas in a liquid increases as the partial pressure of the gas increases

Front 20

Henry's Law - formula

Back 20

Sg = k * Pg
Solubility of gas in liquid = Henry's law constant for liquid/gas combination * Pressure (or partial pressure) of the gas above the solution

Front 21

Molarity (M)

Back 21

number of moles of solute
-------------------------------
number of liters of solution

Front 22

molality (m)

Back 22

moles of solute
------------------
Kg of solvent

Front 23

Colligative properties - definition

Back 23

Properties that depend upon the concentration of particles, not the nature of the particles

Front 24

Colligative properties - examples

Back 24

1. vapor pressure lowering
2. boiling point elevation
3. freezing point depression
4. osmotic pressure

Front 25

Raoult's Law - definition

Back 25

The vapor pressure of any pure solvent will be lowered by the addition of a nonvolatile solute to the solvent

Front 26

Raoult's Law - formula

Back 26

P₁ = X₁*P⁰₁
P₁ - vapor pressure of the solvent over the solution
X₁ - mole fraction of the solvent in the solution
P⁰₁ - vapor pressure of the pure solvent

Front 27

Boiling point elevation - formula

Back 27

ΔTb = Kb*m(solute)

Change in boiling point equals the molal boiling point constant * molality of solute

Front 28

Freezing point depression - formula

Back 28

ΔTf = Kf*m(solute)

Change in freezing point equals the molal freezing point constant * molality of solute

Front 29

Boiling point elevation for electrolytes - formula

Back 29

ΔTb = Kb*m(solute) * i

Change in boiling point equals the molal boiling point constant * molality of solute * number of particles per formula unit (van't hoff factor)

Front 30

Freezing point depression for electrolytes - formula

Back 30

ΔTf = Kf*m(solute) * i

Change in freezing point equals the molal freezng point constant * molality of solute * number of particles per formula unit (van't hoff factor)

Front 31

Osmosis

Back 31

Movement of a solvent through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration

Front 32

Osmotic pressure of a solution - definition

Back 32

The pressure that must be applied to the solution to stop osmosis from a sample of pure solvent

Front 33

Osmotic pressure of a solution - formula

Back 33

π = cRTi
Pressure = concentration (molarity) of solution * gas constant * absolute temperature * i (number of particles per formula unit of solute)

Front 34

Standard Enthalpy of Solution

Back 34

The heat change when one mole of solute is completely dissolved to form a 1 M solution under standard conditions.