previously in chem 104: solutions: macroscopic & microscopic deducing enthalpies of solution...
TRANSCRIPT
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.