Vapor Pressure
Chapter 11 part 3: Phase Changes
Read:
HW:
BLB 11.3, 11.5-11.6
BLB 11:4, 6, 31, 43, 45, 47, 50, 53, 56
Supplemental 11:11-13
Definition:
P=0
Know:
vapor pressure
phase diagrams
P=vapor pressure
time
!!
!"
Which Skill Check Test Bonus Deadline
is Approaching??
__________________________________
rate of evaporation
dynamic equilibrium
(rates are equal)
rate
rate of condensation
When is Exam #3??
________________________________
Locations will be posted on Chem 110 website
When is the Final Exam??
_______________________________________
IGNORE THE ROOMS ON ELION: LOCATIONS
WILL BE POSTED ON THE WEBSITE
Dr. L. Van Der Sluys
Page 1
Chapter 13 part 1
time
Dynamic Equilibrium
forward rate = backward rate
evaporation = condensation
No net change, but change is occurring on
molecular level.
Dr. L. Van Der Sluys
Page 2
Chapter 13 part 1
As T !, what happens to vapor pressure?
1. increases
2. decreases
3. stays the same
Using Kinetic Molecular Theory:
Figure 11.24
As I.M. forces !, what happens to vapor
pressure?
WHY?
Dr. L. Van Der Sluys
Page 3
Chapter 13 part 1
Dr. L. Van Der Sluys
Page 4
Chapter 13 part 1
Phase Diagrams
Boiling Point
Definition:
Plot of pressure vs. temperature of the system
showing the boundaries between the phases.
As Pext !, what happens to boiling point?
1. increases
2. decreases
3. stays the
same
normal boiling point:
boiling point of a liquid when Pext = 1 atm
T at which the v.p. of a liquid is 1 atm.
Know How to Identify the Following;
• normal melting point
• normal boiling point
• critical point
• triple point
• supercritical fluid
• coexistence curves
What happens when the pressure and/or
temperature of the system is changed?
Dr. L. Van Der Sluys
Page 5
Chapter 13 part 1
Dr. L. Van Der Sluys
Page 6
Chapter 13 part 1
Comparison of H2O and CO2 Phase Diagrams
Chapter 13 part 1: Electrolytes
Read:
HW:
BLB 4.1, 4.5; 13.4
BLB 4:3, 15, 37, 61, 71, 72, 73; 13:39, 47;
Supplemental 4:1–3, 13:8-11
Know:
! solutions
! electrolytes
Differences:
1) Triple Point
2) Direction of slant
Melting point line of CO2 slants to the right
with increasing P
MP ___ as P!
Melting point line of H2O slants to the left with
increasing P
MP____ as P!
Water has a liquid form more compact than its
solid form because of the directional
hydrogen-bonded hexagonal structure of ice.
Dr. L. Van Der Sluys
Page 7
Chapter 13 part 1
Dr. L. Van Der Sluys
Page 8
Chapter 13 part 1
Which Bulbs Light Up?
SOLUTIONS
Bulb Wattage
Homogeneous mixture:
25 Watt
40 Watt
Distilled H2O
Solute:
Tap H2O
NaCl(aq)
Solvent:
1M HCl(aq)
1M CH3COOH(aq)
Aqueous solutions:
sugar(aq)
CH3OH
CuSO4
• For bulb to light, some minimum amount of
current is needed.
• amount of current is related to the
CONDUCTIVITY of the solution.
CONDUCTIVITY:
Dr. L. Van Der Sluys
Page 9
Chapter 13 part 1
Dr. L. Van Der Sluys
Page 10
Chapter 13 part 1
The Solution Process
Electrolytes
a) Dissolution of an electrolyte in water
produces solvated ____________. Solvation
stabilizes the ions and prevents
recombination.
DEFINITION:
• Strong – COMPLETELY ionized(in solution)
Good conductors
Example: NaCl
dissociates into ions.
NaCl(s) + H2O " Na+(aq) + Cl# (aq) + H2O
HCl(aq) + H2O " H3O +(aq) + Cl# (aq)
• Weak – PARTIALLY ionized (in solution)
Poor conductors
NH3(aq) + H2O
CH3COOH(aq)+H2O
NH4+(aq) + OH# (aq)
+
CH3COO# (aq)+H3O (aq)
b) Dissolution of a non-electrolyte in
water produces solvated _________________.
Example: CH3OH
• Nonelectrolytes – NOT ionized in solution
Non-conductors
does not
dissociate
C6H12O6(s)+H2O " C6H12O6(aq)+ H2O
glucose
Dr. L. Van Der Sluys
Page 11
Chapter 13 part 1
Dr. L. Van Der Sluys
Page 12
Chapter 13 part 1
Example Problem:
Based on the results of the demo,
which one of the following is a weak
electrolyte?
a) distilled water
b) NaCl(aq)
Identifying an electrolyte
A) Is the compound ionic or molecular?
If Ionic: it is a strong electrolyte
Note: it could be mostly insoluble and
still a strong electrolyte!
If Molecular . . . .
B) If it is molecular, is it an acid or a base?
Yes: it is a strong or weak electrolyte
No: it is a non-electrolyte.
c) 1M HCl(aq)
d) 1M CH3COOH(aq)
e) sugar(aq)
Examples of electrolytes (strong or weak)
Acids donate H+(aq)
Bases accept H+(aq)
Salts formed by replacing one or more
H+ of an acid with another cation
f) CH3OH(aq)
Examples of non-electrolytes:
Examples of WEAK electrolytes:
Weak Acids (including ______________)
Weak Bases (including ______________)
Dr. L. Van Der Sluys
Page 13
Chapter 13 part 1
Dr. L. Van Der Sluys
Page 14
Chapter 13 part 1
Strong or weak electrolyte?
Ionic compounds:
1) Assume all salts are strong electrolytes.
2) Memorize 7 strong acids and groups of
strong bases; all are strong electrolytes.
Metal + nonmetal (usually)
Ex: NaCl
K2SO4
Mg(NO3)2
NH4Cl
What can you say about the melting points
of ionic compounds?
Molecular compounds:
All nonmetals or nonmetals & metalloids.
Ex: HCl
H 2O
CH3COOH
NH3
If a compound is an acid or a base, but is
NOT one of the strong acids or bases,
what MUST it be?
What can you say about the melting points
of molecular compounds?
Dr. L. Van Der Sluys
Page 15
Chapter 13 part 1
Dr. L. Van Der Sluys
Page 16
Chapter 13 part 1
Common misconception:
"All Electrolytes are ionic compounds"
NOT TRUE!
• Strong electrolytes – ionic or molecular
compounds that ionize completely in
solution.
Which one of the following is an ionic
compound?
A.
B.
C.
D.
H2 O
NH4Cl
CH3COOH
NH3
• Weak electrolytes– molecular compounds
that are partially ionized in solution.
• Nonelectrolytes – molecular compounds
that do not ionize in solution
Is HCl a molecular or ionic compound?
A. molecular
B. ionic
Which of the following is/are a weak
electrolyte(s)? A=WEAK, B=STRONG
HBr
NH4Cl
CH3CH2COOH
NH3
Dr. L. Van Der Sluys
Page 17
Chapter 13 part 1
Dr. L. Van Der Sluys
Page 18
Chapter 13 part 1
These are all water soluble compounds. Are
they strong, weak or non electrolytes?
Electrolyte Flowchart
Water soluble
Compound
molecular
A=WEAK, B=STRONG, C=NON
Use the Flowchart on the previous page
ionic
HCl
Is it an acid?
NaCl
Yes
No
Is it a strong acid?
Yes
Strong
electrolyte
Is it a molecular base?
(eg. NH3)
no
yes
Strong
Electrolyte
CH3COOH
(acetic acid)
NH3
Fe(NO3)2
weak
electrolyte
Dr. L. Van Der Sluys
no
weak
electrolyte
CH3OH
Page 19
non electrolyte
Chapter 13 part 1
Ca(OH)2
Dr. L. Van Der Sluys
Page 20
Chapter 13 part 1