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- Instructor: Upali Siriwardane (Ph.D., Ohio State University)
- CTH 311, Tele: 257-4941, e-mail: upali@chem.latech.edu
- Office hours: 10:00 to 12:00 Tu & Th ; 8:00-9:00 and 11:00-12:00 M,W,& F
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- Tests will be given in regular class periods from 9:30-10:45
a.m. on the following days:
- September 22, 2004 (Test 1): Chapters 1 & 2
- October 8, 2004(Test 2): Chapters 3,
& 4
- October 20, 2004 (Test 3):
Chapter 5 & 6
- November 3, 2004 (Test 4):
Chapter 7 & 8
- November 15, 2004 (Test 5): Chapter
9 & 10
- November 17, 2004 MAKE-UP: Comprehensive
test (Covers all chapters
- Grading:
- [( Test 1 + Test 2 + Test3 +
Test4 + Test5)] x.70 + [ Homework + quiz average] x 0.30 = Final Average
- 5
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- Describe the behavior of gases : Boyle's law, Charles's law, combined gas law,
Avogadro's law, the ideal gas law,
and Dalton's law.
- 2. Use gas law equations to calculate conditions and changes in
conditions of gases.
- 3. Describe the major points of the kinetic molecular theory of gases.
- 4. Explain the relationship between the kinetic molecular theory and the
physical properties of macroscopic quantities of gases.
- 5. Describe properties of the liquid state.
- 6. Describe the processes of melting, boiling, evaporation, and
condensation.
- 7. Describe the dipolar attractions known collectively as London dispersion (van der Waals)
forces.
- 8. Describe hydrogen bonding and its relationship to boiling and melting
- temperatures.
- 9. Relate the properties of the various classes of solids (ionic,
covalent,
- molecular, and metallic) to the structure of these solids.
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- By changing the temperature (and pressure) all matter can exist as a
solid, as a liquid and as a gas.
- There are forces of attraction (which we learn about later) btn cmpds
that determine what physical state (gas, liquid, solid) we find the cmpd
in at a given temperature.
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- Temperature gives molecules kinetic energy. ______ the temp the ________
the kinetic energy.
- If the strength of attractive forces btn
molecules is much larger than the kinetic energy due to temp the cmpd
will be a ________
- If the molecules’ kinetic energy due to temp is much greater than the
attractive forces btn molecules the cmpd will be a _______
- If the attractive forces and the energy due to temp are similar the cmpd
will be a _______
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7
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8
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9
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- 4. In general for the same substance
density of a solid > density of a liquid > density of a
gas
- For water densityliquid > densitysolid (ice floats)
- See table 6.1
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- We are going to describe a gas in terms of the pressure (P) it exerts,
the volume (V) it occupies and its temperature (T).
- Pressure is a
- We live at the bottom of a sea of gas molecules which are constantly
hitting us and exerting pressure on us.
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- The downward force on any surface area (say 1 in2)due to
“air” is equal to the mass of the column of air above the area and is
14.7psi (lb/in2).
- We measure the pressure of the atmosphere with a
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- Pair = PHg in the barometer tube. The downward
pressure of the mercury in the column is balanced by the outside
atmospheric pressure pressing down on the mercury in the dish.
- We define one atmosphere as the atmospheric pressure which
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- 1 atm =
- (1 torr = 1 mm Hg)
- Express 528 mm Hg in atm
- Express 2.86 atm in mm Hg and torr.
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- 4 easily measured macroscopic properties: V, T, P, n (# moles)
- Now we want to develop a mathematical relationship btn P,V,T and the no.
of moles (n) of a gas.
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- Boyle (1660) did some experiments that showed as the pressure applied to
a gas increases, the volume occupied by the gas decreases as long as the
temperature and amt of gas is held constant.
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- or P µ 1/V and V µ 1/P
- PV = k1 where k1 is a proportionality constant
that is
- PiVi = k1 and PfVf
=k1 so
- PiVi = PfVf at the same temp and no.moles of
gas
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- Gases follow Boyle’s law best (PV=k) at
- .
- complete Pi(atm)
Pf(atm) Vi(L) Vf(L)
- 1.0 0.50 ? 0.30
- 1.0 2.0 0.75 ?
- What happens to the volume if you triple the pressure at constant temp
and no. moles?
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- Charles, a hot air balloonist, (1800’s) investigated how V and T
(temperature in K) were related.
- He found that as the temperature of the gas increased, the volume
occupied by the gas also increased as long as the pressure and amt of
the gas were held constant.
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- or V µ T and V = k2T where k2
is a proportionality constant that depends on the
- Remember to convert from oC
to K
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- V = k2T
- V/T = k2
- k2 = proportionality constant
- independent of identity of gas
- requires constant P and n
- Vi/Ti = k2 and Vf/Tf
= k2 so
- Vi/Ti = Vf/Tf
- excellent approximation at
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- What happens to the volume when the temp in Kelvin is tripled at
constant P and n?
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- Avogadro found that the volume of a gas increased as the amt of the gas
increased when the pressure and temp were held constant. (balloon)
- V µ n or V = k3n direct
relationship
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- V µ n
- V = k3n
- V/n = k3
- Vi/ni = Vf/nf
- holds best at
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- Equal volumes of gases under the same conditions of temp and pressure
contain equal nos. of particles.
- Equal moles of all gases under
the same conditions of temp and pressure have the same volume.
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- Boyle: V µ 1/P
- Charles: V µ T
- Avogadro: V µ n
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- An ideal gas obeys the gas laws we have developed. A real gas may deviate somewhat from
these laws. But under conditions of _____________________, these laws
are obeyed. The reason for this will be discussed later.
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- STP (standard temp and pressure)
- It is found that 1 mol of a gas occupies a volume of
- Substituting the molar volume at STP in PV=nRT
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- V of one mole of gas at STP = 22.4 L
- Same V regardless of identity of gas!
- but
- 22.4 L of N2
- 22.4 L of CH4(g)
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- d =
- At STP
- 1 mol of H2 has a mass of 2.0 g so dH2 =
- 1 mol of O2 has a mass of 32.0 g so dO2 =
- 1 mol of CO has a mass of 28.0 g so dCO =
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- The ideal gas law contains all the other laws.
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- The temp has to be in
- In the comparative laws (Boyle’s, Charles’, etc) pressure and volume
just have to be in the same units. n has to be in moles
- In the ideal gas law the units
are as specified before.
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- A sample of nitrogen gas kept in a container of volume 2.3L and at a
temp of 32oC exerts a pressure of 4.7 atm. Calc the no. of
moles and the mass of gas
present.
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- A balloon has a volume of 43.0L at 20oC. What is its volume
at -5oC?
- A syringe has a volume of 10.0mL at 14.7psi. If the tip is blocked so
that air can’t escape, what pressure is required to decrease the volume
to 2.00mL?
- If 20.0g of N2 gas has a volume of 4.00L and a pressure of
6.00atm, what is its temp?
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- Which sample contains more molecules: 2.0L of CO2 at 300K and
500 mm Hg or 1.5L of N2 at 57oC and 760 mm Hg?
Which sample weighs more?
- An aerosol can has an internal pressure of 3.75atm at 25oC.
What temp is required to raise the pressure to 16.6atm?
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- A compressed-air tank carried by scuba divers has a volume of 8.0L and a
pressure of 140 atm at 20oC. What is the volume of air in the
tank at 0oC and 1.00atm pressure (STP)?
- Cyclopropane. C3H6,
is used as a general anesthetic. If a sample of cyclopropane is stored
in a 2.00 L container at 10.0 atm and 25.0oC is transferred
to a 5.00 L container at 5.00 atm, what is its resulting temp?
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- What is the effect on a gas if you simultaneously:
- a) halve its pressure and double its Kelvin temp
- b) double its pressure and double its Kelvin tempereature.
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- What volume will 818 g of sulfur hexafluoride gas occupy if the
temperature and pressure of the gas are 128oC and 9.4 atm?
- At what temp will 2.00 mol He fill a 2.00 L container at STP?
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- 6.34: How many grams of helium must be added to a balloon containing
8.00 g of helium gas to double its volume. Assume no temp or pressure
change.
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- Dalton (1803) said in a mixture of gases, each gas exerts a pressure as
if it were present alone in the container. The pressure each gas exerts
is called
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- For gas mixtures
- Partial Pressure –pressure of an individual gas component in a mixture
- Dalton’s Law of Partial Pressure – total pressure of a mixture of gases
is the sum of the pressures that each gas would exert if it were present
alone
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- The mixture of gases as well as each gas obeys the ideal gas law and all
of the other laws.
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- The partial pressure of CH4(g) is 0.225atm and C2H6(g)
is 0.165 atm in a mixture of the
two gases. What is the total pressure?
- A gas mixture has three components, N2, O2 and He.
If the total pressure of the mixture is 0.78 atm and the partial
pressure of N2 and He are 0.40 atm and 0. 18 atm
respectively, what is the partial pressure of the O2 in the
mixture?
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- There are several basic hypotheses that are used to explain the behavior
of gases.
- 1.Volume occupied by gas molecules themselves is negligible compared to
the total volume occupied by the gas itself. (Gas molecules are though
of as point masses: have mass but occupy no volume.)
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- 2.The molecules of a gas are in constant, rapid, random straight line
motion (Brownian motion) with no attractive forces btn the the
molecules.
- 3.The collisions the molecules make with themselves and with the walls of the container are elastic
collisions. In other words energy is transferred from one molecule to
another in a collision but the total energy of the molecules stays the
same.
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- 4. At a given time the gas molecules have different speeds and different
kinetic energies but the average kinetic energy of all the molecules of
the gas is directly proportional to the Kelvin temperature(T).
- KEaverage µ T or
- KEaverage = cT where c is a constant
- Note that as
- Gases that obey these assumptions are known as
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- Zero volume?
- No attractive forces?
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- How explain compressibility, expand, low density, diffusion
- KE = 1/2mv2
- At the same temp, molecules with
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- Back to end of chapter 4 and review polar vs nonpolar
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- Now what are these intermolecular forces we mentioned earlier.
- Intermolecular forces are forces btn different molecules. Intramolecular
forces are forces btn atoms in a bond (of the order of 200-500
kJ)--generally much stronger than intermolecular forces.
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- Stronger intermolecular force,
the _______ the boiling and melting points
- What are these forces?
- I. ion-ion forces:
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- II.Dipole-dipole forces: forces that operate when have ______ molecules.
In general, the more polar the molecule (larger the difference in
electronegativities), the stronger the forces.
- These forces (dipole-dipole) are of the order of 5 to 20 kJ/mol. Cmpds
that have these forces (dipole-dipole) are frequently
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- III. London (dispersion) forces: used to explain intermolecular forces
in
- Electrons in molecules are constantly moving.
- On the average, in a nonpolar molecule the electrons are evenly
distributed leading to an overall equal sharing throughout.
- But since electrons are moving,
at some instance in time there is an unequal distribution and an
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- This instantaneous dipole induces a dipole in neighboring molecules,
creating an interaction btn molecules.
- This interaction is relatively weak (0.1-5 kJ).
- London and dipole-dipole forces are known collectively a
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- Remember as strength of forces increase have higher m and b pts.
- Therefore
- and
- and
- Notice that we are comparing like species,
- But what about HF, HCl, HBr, HI and H2O, H2S, H2Se,
H2Te and NH3, PH3, AsH3
and SbH3.
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- Explain these anomalies by a “new” force called
- Requirements for hydrogen bonding:
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- Water forms 4 hydrogen bonds per molecule, HF and NH3 only
one.
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- Dimethyl ether (CH3OCH3) and ethanol (C2H5OH)
have the same formula (C2H6O) but the b pt of the
ehter is -25oC and of the ethanol 78oC. Explain.
- Which of these form hydrogen bonds?
- CH3OH
- C2H4
- CH3NH2
- HCN
- NH4+
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- In general ionic forces the strongest, then hydrogen bonding,
dipole-dipole and lastly dispersion for species of similar molar mass.
- N2 (bpt -195oC)
O2 (bpt -183oC)
- N2 (bpt -195oC)
CO (bpt -190oC)
H2O (bpt 100oC)
- CH3F (-141.8oC)
CCl4 (-23oC)
- NaCl (801oC mp)
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- Put a lid on a container filled with a liquid so have closed system.
- Find some of the molecules in the liquid phase have enough KE to escape
from the surface of the liquid and form a vapor phase.
- At the same time some of the gas molecules in the vapor phase fall back
into the liquid.
- evaporation
- Liquid
gas
- condensation
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- At some point in time the
- Say we have reached a state of dynamic equilibrium.
- Pressure exerted by the vapor (gas molecules) above the liquid is called
the equilibrium _________________
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- The value of the vapor pressure depends on
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- Normal b pt: temp at which the v.p. of the liquid =
- Boiling pt depends on strength of intermolecular forces.
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- Which will have the greater vapor pressure at 5oC? The higher
b pt?
- CH3OCH3 or CH3CH2OH
- CH4 or CCl4
- I2 or Cl2
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- Compressibility: increased pressure essentially no effect on liquids and
solids--brake fluid
- Viscosity: resistance to flow; stronger intermolecular forces, greater
viscosity; viscosity decreases with increase in temp.
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- Surface tension: measure of attractive forces at surface of
liquid--leads to sperical shape of drops of liquid
- Surfactant (soaps and detergents): decrease surface tension--grease
removal
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- Properties: virtually incompressible
- Melting point: temp at which change into liquid--depends on strength of
intermolecular forces
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- Crystalline solids: regular repeating order in 3D structure
- Types of crystalline solids
- 1. Ionic solids:
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- 2. Covalent (network )solids:
- 3. Molecular solids:
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Notes
