Previously in Chem 104: Solutions: macroscopic & microscopic Deducing Enthalpies of Solution Energetics (Enthalpies) of Dissolution— they can be exo-

Previously in Chem 104:

• Solutions: macroscopic & microscopic

• Deducing Enthalpies of Solution

• Energetics (Enthalpies) of Dissolution—they can be exo- and endothermic

TODAY• QUIZ answer key out - send self-check by Tuesday midnight

• Another BIG IDEA- Equilibrium

• Effects on Dissolution by:

• P• T

• Effects of Dissolution on:

• vapor pressure• boiling• freezing

A really BIG IDEA in chemistry

A really BIG IDEA in chemistry

Closely followed by

We need another word to pair with

Dynamic

As applied to a solid in equilibrium with a solvent in solution:

Combined with

Example 1.This explains phase changes in phase diagrams

“ a system at equilibrium when disturbed will adjust to remove or minimize the effect of the disturbance”

H2O Phase Diagram

Temperature, deg C

Pre

ssu

re,

atm

solid liquid

gas

0deg

1 atm

ice water

H2O Phase Diagram

Temperature, deg C

Pre

ssu

re,

atm

solid liquid

gas

0 deg

1 atm

ice

makemorewater

5 atm

meltslower T

Combined with

This explains almost all Solution behaviorsExample 2. How gas pressure affects solubility

Sg = kh PgGas solubility depends on gas partial pressure Sg = kh Pg

Henry’s Law Constant

A related example: How temperature affects gas solubility

Increase T and:

Combined with

Explains almost all Solution behaviors

Gas + solvent Gas solution + energy (exothermic)

Gas + solvent Gas solution + energy

Another related example: How temperature affects solid solubility

Increase T and:

Combined with

Explains almost all Solution behaviors

Case A. MX + water M-(aq) + X-(aq) + energy

MX + water M-(aq) + X-(aq) + energy

Less dissolves

Increase T and:

Case B. MX + water + energy M-(aq) + X-(aq)

MX + water + energy M-(aq) + X-(aq)

More dissolves

Combined with

Explains almost all Solution behaviors

Example 3. How a solute affects solvent vapor pressure

Psolvent = Xsolvent Posolvent

Combined with

Explains almost all Solution behaviors

Example 3. How a solute affects gas pressure

Psolvent = - Xsolute Posolvent

Combined with

Explains almost all Solution behaviors

Example 4. How a solute affects solvent boiling point

Tbp = Kbp msolute

When does a liquid boil?

Lower vapor pressure, requires more energy,higher T, to get to atmospheric pressure: Boiling Point Elevation

What changes if we add a solute?

Ebullioscopic constant

Tbp = Kbp msolute

Combined with

Explains almost all Solution behaviors

By extension: How a solute affects solvent freezing point

Tfp = Kfp msolute

Combined with

Explains almost all Solution behaviors

Three examples of Colligative Properties:colligative – depends only on the number of particles

Tfp = Kfp msolute

Tbp = Kbp msolute

Psolv = Xsolvent Posolvent

Tfp = Kfp msolute

Tbp = Kbp msolute

Psolv = Xsolvent Posolvent

Calculations based on Colligative Properties:requires different concentration units

M, molarity = #moles solute / liter solvent

m, molality = #moles solute / kg solvent

Weight % = (mass A/ total mass) x 100%

Mole fraction= #moles A / total # moles

We need to deal with concentration expressed as mole fraction, molality because collogative propertiesdeal only with number of particles in solution, not identities.