Chapter 12
Compressibility
Shape
Volume
Gaseous State of Matter
Solid
N
Y
Y
Liquid
N
N
Y
Gas
Y
N
N
Gas molecules move freely until they hit the wall.
Unlike liquids, gases expand to fill the container.
An Ideal Gas consists of point-like particles
that do not attract or repel one another at all.
When air is removed from a can, there are no gas
molecules to oppose the atmospheric pressure
exerted from the outside, so the can collapses.
Air pump
Pressure =
Force
= Area
Pressure can be measured by the height
of mercury column. When air is removed
from the tube, there is no resistance to
the flow of mercury from the bottom
container. Mercury fills the tube until the
atmospheric pressure is compensated
by the weight of mercury column.
We do not feel atmospheric pressure due to
random motion of air. But you feel the wind!
Pressure imbalance in ear: A difference in
pressure across the eardrum membrane
causes the membrane to be pushed out –
we call it a “popped eardrum.”
Gas Pressure
Normal atmospheric pressure:
1 atm = 760. mm Hg = 760. torr
= 29.9 in Hg.
Behavior of an ideal gas can be totally described
with pressure (P), volume (V), temperature (T) and
the number of moles of gas (n).
Pressure (P) – atmospheres
Temperature (T) – Kelvin
Volume (V) – liters
Amount of Gas (n) – moles
If different units are
given, convert them
into atm, K, L, moles
Describing the Gas
Volume is directly proportional to
Pressure (P) proportional to temperature (T). temperature (Charle’s Law): V α T
Faster moving gas molecules exert higher
Pressure is inversely proportional to
pressure on the walls of the container (Guythe volume (or proportional to 1/V).
Lussac’s Law).
As the volume increases, pressure
PαT
decreases (Boyle’s Law).
T in K!
P α 1/V
α means proportional.
Pressure is proportional to the number of
moles of gas. More gas molecules results in
more collision with the walls of the container.
Pαn
P α nT/V or P = const. x
P=R
nT
V
nT
V
PV = nRT
R = 0.0821 L atm Ideal gas law
mol K
R is called ideal gas constant, and is
the same for any gas.
Dalton’s Law of Partial Pressures
Ptotal = PA + PB + PC + …
The total pressure of a mixture of gases is
the sum of the partial pressures exerted
by each of the gases in the mixture.
When collecting oxygen over water (usual
way), water vapor contributes to the total
pressure. To determine the amount of O2, the
water vapor pressure must be subtracted form
the total pressure.
PO2 = Ptot – PH2O
Standard temperature and pressure (STP) is (exactly) 1 atm and 0oC.
Avogadro’s Law
Equal volumes of different gases at the same T, P contain the same number of
molecules.
Different gases at the same P, T have equal kinetic energy, and since they occupy the same
volume, they must have the same number of molecules to satisfy the relationship PV = nRT.
1 mol of ANY gas occupies 22.4 L at STP.
If the mass and volume of the gas at
STP are known, one can calculate the
molar mass M.
Since M = mass / number of moles,
M=m/n n=m/M
Substituting in Ideal Gas Law:
m
mRT
PV = nRT PV = RT
M=
M
PV
Gas volume depends on the T and P.
Density of Gases
Density is: mass / volume and for a gas is expressed in g/L.
Recall that densities of solids and liquids are given in g/mL!
Gas densities are up to 1000 times lower than the densities of their liquids.
Ideal Gases
Most real gases behave nearly as
predicted by the ideal gas law.
Real Gases
Deviations occur when molecules
are crowded (high P, low T).
Air Pollution
oxygen
Oxygen allotrope ozone is produced and
decomposed in stratosphere; the latter
protects us from damaging UV light.
Simultaneous processes occur:
sunlight
ozone
O2
O+O
O2 + O O3
O3
Ozone formation
Ozone decomposition
UV light
O2 + O
Chlorofluorocarbons in aerosols and refrigerators (now
banned) decompose ozone producing ozone hole.
Ozone hole is now over
Antarctica but could spread
over populated areas.
Global warming
Green house gases (CO2, methane, water) warm atmosphere by trapping heat
near the surface of the Earth.
- Concentration of CO2 in air due to fossil
fuels combustion steadily rises since
industrial revolution (end of 1800s); only
in last 50 years it has risen over 25%.
- Concentration of methane in air,
produced by agriculture and cows,
almost doubled in the last 50 years.
Chapter 13
Water and Properties of Liquids
Liquids have intermediate properties between solids
and gases. Liquids are almost incompressible, have
definite volume and assume the shape of the container.
Densities of
liquids are
usually lower
than that of their
solids. Water is
an exception.
Evaporation or vaporization is the escape of
molecules from liquid into gaseous state.
During evaporation, liquid that stays behind is
cooler. The opposite process is condensation.
Sublimation is the escape of molecules directly
from solid into gas, bypassing liquid state.
Vapor pressure is the pressure exerted by a gas at
evaporation
equilibrium with its liquid, so that:
liquid
gas
Vapor pressure depends only on
condensation
temperature, not on the amount of
liquid.
Open container
completely evaporates.
Closed container
reaches equilibrium
between liquid and gas.
Vapor Pressure Measurement
1 atm = 760 torr
20 oC
20
oC
a.
b.
a. The system is evacuated.
Manometer attached to the
flask shows equal pressure
in both legs.
b. Water is added.
Liquid evaporates.
Manometer shows
increase in pressure.
20 oC
30 oC
c.
d.
c. Equilibrium established.
Manometer shows constant
pressure difference, 17.5 torr.
d. Temperature raised to 30 oC.
Equilibrium reestablished.
Manometer shows constant
pressure difference of 31.8 torr.
Vapor pressure
and temperature
1 atm = 760 torr
Vapor pressure of any
gas at the boiling point
is equal to the
atmospheric pressure.
Vapor pressure of
ethyl ether is the
highest at any temp.
TBP
TBP
Vapor pressure:
Ether > Alc. > Water.
Rate of evaporation:
Ether > Alc. > Water.
proportional to vapor
pressure.
TBP
Volatility
Boiling point:
Ether < Alc. < Water
Substances that readily evaporate are volatile.
Vapor pressure of ethyl ether at 20 oC: 442.2 torr
Volatile
Vapor pressure of water at 20 oC: 17.5 torr
Vapor pressure of mercury at 20 oC: 0.0012 torr
Moderately volatile
Nonvolatile
Boiling Point Curves
Normal Boiling Point
Boiling point at standard pressure
(1 atm, or 760 torr).
Each point on the curve represents a
vapor-liquid equilibrium at a
particular temperature and pressure.
At 500 torr, ethyl ether boils at
~22 oC, alcohol at ~68 oC, and
water at 89 oC.
Freezing or Melting Point
The temperature at which the solid
and liquid are in equilibrium.
Changes of State
Majority of substances change phases
upon heating: solid liquid gas.
1 atmosphere
pressure
TBP ethyl ether
TBP alcohol
TBP water
34.6oC
78.4oC
100.0oC
Heating curve for a pure
substance
CO2 is an exception (dry ice sublimes).
A – B: solid state
B – C: melting
C – D: liquid state D – E: evaporation
E – F: vapor state
Temperature is constant during melting
and boiling – all heat used to break
solid (at boiling point) or liquid forces.
liquid
solid
evaporation
condensation
melting
freezing
gas
liquid
Heat of Fusion and Heat of Vaporization
We learned before that amount of heat
Qheating = (mass) (spec.heat) (temp.change)
depends on mass and temp. change.
Energy (heat) needed to change 1 g
Energy (heat) needed to change 1 g
of a solid at its melting point into Constant
of a liquid at its boiling point into
liquid is heat of fusion.
temperature! vapor is heat of vaporization.
Qfusion = (mass) (spec.heat of fusion)
Qvaporization = (mass) (spec.heat of vaporization)
Solid and liquid at the melting point, or liquid and gas at boiling pt. have different energy.
Intermolecular forces
+ -
+ -
+ + 1. Dipole-dipole interaction occurs among polar
+ covalent molecules with separate partial
electrical charges and no center of symmetry
falling on the central atom. HCl is polar, CO2 and CH4 are not.
2. Hydrogen Bond produces unusually high melting & boiling point
δδ+
H Cl
δ+, δO C O
Hydrogen Bonding (cont.)
H bonding exists between H directly bonded
to one of the three most electronegative
elements (Fluorine, Oxygen, and Nitrogen),
and F, O or N of another molecule.
. . H bond . .
H – O :. . . H – O :
|
|
H
H
H
bonded
to O
No H bond
H
H
| .. |
H–C–O–C-H
| .. |
H
H
Ethyl ether
3. London Dispersion Forces
δ+
δ-
δ+
δ-
Strength of LDF
increases with the
increase of molecular
mass M. He (M=4)
freezes at -272 oC,
and paraffin (M=352)
is solid at room temp.
Nonpolar molecules
have instantaneous,
short-lived polarity (δ+/δ-)
due to distribution of
electrons. This short
lived polarity induces
polarity on the
neighboring atom,
attracting it: These
forces are called LDF.
No H bonded
to F, O, or N
H bonds are
intermolecular
forces.
Hydrates
Some ionic solutions retain water upon evaporation. It becomes
the part of the crystalline compound – water of crystallization.
The formula is written as: ionic compound, dot , # water molecules…
CuSO4 5 H2O and name them by adding # (Latin) hydrate.
.
Copper(II) sulfate pentahydrate.
Hydrates are true compounds and the water is an integral part of it.
Formula mass CuSO4 5 H2O: 63.55+32.07+64.00+5x18.02 = 249.7
Percent composition of water is (5x18.02 / 249.7) x 100 = 36.08%
dry CuSO4 – white
Hydrate = blue
.
Water can be removed by intense heat: CuSO4
The reaction is reversed when water is added.
Water, a Unique Liquid
Water indicator
. 5 H O(s) CuSO (s) + 5 H O(g)
2
4
2
δO
H
H
Water covers ~75% of Earth. 97% of water is in the oceans. Only
3% is fresh water, of which 2/3 is locked up in ice polar caps.
δ+
Solid form (ice) has lower density than liquid water.
Water is very stable molecule, can stand temperatures up to 2000 oC. It does not
conduct electricity when pure, but decomposes into H2 and O2 in solutions of ions.
2 H2 + O2 --> 2 H2O + 484 kJ
Water can be formed by
2 C2H2(g) + 5 O2 4 CO2 + 2 H2O(l) + 1212 kJ
Combustion,
Neutralization,
HCl(aq) + NaOH(aq) --> NaCl(aq) + 2 H2O
Metabolic reaction
C6H12O6(aq) + 6 O2 6 CO2(g) + 6 H2O(l) + 2519 kJ
Water reactions with metals:
Cold water reacts with Na, K, Ca:
Steam reacts with Zn, Al and Fe:
Reactions of water
Na + H2O H2 + NaOH
Fe + H2O(g) --> H2 + Fe3O4
Remind yourself of the activity series: the above six metals are the most active. Another
three metals are more active than H: Pb, Sn, and Ni and react with acids only; Cu, Ag,
Hg and Au are below H in the series and do not react with acids or H2O.
Water also reacts with metal oxides as well as with
nonmetals and nonmetal oxides, producing acids
and bases.
Acid formation:
2 F2 + 2 H2O(l) --> 4 HF(aq) + O2
Some substances are
called anhydrides. It
means: without water.
Try to remove H2O until all
hydrogen is removed.
CO2(g) + H2O(l) H2CO3(l)
Base formation:
CaO + H2O(l) Ca(OH)2(aq)
Water Purification
Screening, flocculation and sedimentation,
sand filtration, aeration, disinfection.
Hard water contains Mg2+ and Ca2+ ions
Additional water purification is done by
distillation, Ca2+, Mg2+ precipitation, ion
exchange and demineralization.
Ca
OH ∆
OH
CaO + H2O
H2SO4 ∆ SO3 + H2O
HW, Chp.12 (p.277): 13, 17, 21, 52
13. A sample of gas occupies a volume of
1025 mL at 75 oC and 0.75 atm. What
will be the new volume if the
temperature decreases to 35 oC and
pressure increases to 1.25 atm?
17. A 775 mL sample of NO2 gas is at STP.
If the volume changes to 615 mL and
the temperature changes to 25 oC,
what will be the new pressure?
21. A mixture contains H2 at 600. torr
pressure, N2 at 200. torr pressure, and
O2 at 300. torr pressure. What is the
total pressure of the gases in the
system?
52.Explain why is it necessary to add air to
a car’s tires during winter.
59.What volume does 1 mol of an ideal
gas occupy at STP?
.
HW, Chp.13 (p.302): 5, 11 13, 21
5.In which of the following substances
would you expect to find hydrogen
bonding? C3H7OH; H2O2; CHCl3; PH3;
HF.
11.Name these hydrates: BaBr2 · 2 H2O;
AlCl3 · 6 H2O; FePO4 · 4 H2O.
13.How many moles of compound are in
25.0 g of Na2CO3 · 10 H2O?
21. How many joules of energy are
needed to change 275 g of H2O from
15 oC to steam at 100 oC?
.