Aldehydes and Ketones Bettelheim, Brown, Campbell and Farrell Chapter 17.
Gases, Liquids and Solids Bettelheim, Brown, Campbell and Farrell Chapter 5.
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Transcript of Gases, Liquids and Solids Bettelheim, Brown, Campbell and Farrell Chapter 5.
Gases, Liquids and Solids
Bettelheim, Brown, Campbell and Farrell
Chapter 5
• Overview
• Phase Changes
• Gases
• Intermolecular Forces– London Dispersion, Dipole-dipole,
Hydrogen-bonding
• Liquids
• Solids
State characteristics
• Gases– No definite shape or volume; flows– Particles far apart; no interactions
• Liquids– Definite volume, no fixed shape, flows– Particle in contact; moderate interactions
• Solids– Definite shape, volume; does not flow– Particles in contact; strong interactions
Solid Liquid Gas
All particles Particles Particles dotouching touching not touchNo empty Some open Lots of emptyspaces spaces space betweenbetween between themthem themStrong Moderate NoInteractions interactions interactions
Changes of StateMelting: Change from solid to liquid state + heatFreezing: Change from liquid to solid state - heat
Evaporation: Change from liquid to gas state + heatCondensation: Change from gas to liquid state - heat
Sublimation: Change from solid to gas state + heat (Skips liquid state)
Deposition: Change from gas to solid state - heat (Skips liquid state)
Changes of State
• Heat of Fusion: The amount of heat needed to change 1 g of a substance from the solid to the liquid state (at melting point)
• Heat of Vaporization: The amount of heat needed to change 1 g of a substance from the liquid to the gaseous state (at boiling point)
Heat and Phase Changes
• Example: Naphthalene, an organic substance often used in mothballs, has a heat of fusion of 35.7 cal/g. How much heat, in kilocalories, is required to melt 38.4 g of naphthalene?
Heat and Phase Changes
• Example: Naphthalene, an organic substance often used in mothballs, has a heat of fusion of 35.7 cal/g and a molar mass of 128.0 g/mol. How much heat, in kilocalories, is required to melt 0.300 mol of naphthalene?
Phase Changes• The heating curve of ice
Heat of fusion
Heat of vaporization
Kinetic Molecular Theory of Gases
• Gas particles have negligible volume compared to volume gas occupies
• No attraction between particles • Particles move through space in straight lines • Kinetic energy (KE) proportional to temperature (K)• Can collide with container or each other• Total KE before collision = KE after collision• Collisions with walls of container exert pressure
Gases
• Gas pressure:Gas pressure: the force per unit area exerted against a surface– most commonly measured in millimeters of
mercury (mm Hg), atmospheres (atm), and torr
1 atm = 760 mm Hg = 760 torr = 101,325 pascals = 28.96 in. Hg
Gas PressureA mercury
barometer
Gas Laws
• Boyle’s law:Boyle’s law: Volume and pressure are inversely proportional (fixed mass and gas at a constant temperature
PV = constant or P1V1 = P2V2
Gas Laws
Charles’s Law:Charles’s Law: Temperature and volume are directly proportional (fixed mass and pressure); Temperature is in kelvins (K)
VT
V1
T1
V2
T2
= a constant or =
Gas Laws• Gay-Lussac’s Law:Gay-Lussac’s Law: Pressure and
temperature are directly proportional (fixed mass and volume); Temperature in kelvins (K)
PT
P1
T1
P2
T2
= a constant or =
Combined Gas Law• Boyle’s law, Charles’s law and Gay-
Lussac’s law can be combined into one law called the combined gas lawcombined gas law
P1V1
T1
P2V2
T2
PVT
== a constant or
Gas Laws
• Problem:Problem: a gas occupies 2.00 L at 5.00 atm. Calculate its volume when the pressure is 10.0 atm. (Assume no change in temperature.)
Gas Laws
• Problem:Problem: a gas occupies 2.00 L at 5.00 atm. Calculate its volume when the pressure is 10.0 atm. (Assume no change in temperature.)
Gas Laws
• Avogadro’s law:Avogadro’s law: volume of gas is directly proportional to its molar amount at a constant pressure and temperature– Volume number of moles (n)
V/n = constant
– One mole of ANY gas at STP occupies 22.4 L– Standard temperature and pressure (STP)
are 0°C (273 K) and 1 atm pressure
Ideal Gas Law
• Ideal gas law: Ideal gas law: Can be used for a single sample that does not change
PV = nRT
P = pressure of the gas in atmospheres (atm)
V = volume of the gas in liters (L)
n = moles of the gas (mol)
T = temperature in kelvins (K)
R = ideal gas constantideal gas constant (a constant for all gases)
Ideal Gas Law
• The value of R is determined using the fact that one mol of any gas at STP occupies 22.4 L
– Problem:Problem: 1.00 mol of CH4 gas occupies 20.0 L at 1.00 atm. What is the temperature of the gas in kelvin?
PVR =nT
= (1.00 atm)(22.4 L)(1.00 mol)(273 K)
= 0.0821 L•atmmol•K
Ideal Gas Law
– Problem:Problem: 1.00 mol of CH4 gas occupies 20.0 L at 1.00 atm. What is the temperature of the gas in kelvin?
Ideal Gas Law
– Problem:Problem: 1.00 mol of CH4 gas occupies 20.0 L at 1.00 atm. What is the temperature of the gas in kelvin?
Gas Laws• Dalton’s law of partial pressures:Dalton’s law of partial pressures: the total
pressure, PT, of a mixture of gases is the sum of the partial pressures of each individual gas
PT = P1 + P2 + P3 + . . .
• A tank contains N2 at 2 atm and O2 at 1 atm. If we add CO2 until the total pressure is 4.6 atm, what is the partial pressure of CO2?
4.6 atm 2.0 atm 1.0 atm 1.6 atmTotal
pressurePartial pressure
of N2
Partial pressure
of O2
Partial pressureof CO2
+ +=
Intermolecular Forces
• Forces between molecules affect physical properties such as:– Boiling point (bp)– Melting point (mp)– Solubility
Intermolecular Forces
– Occurs because of electrostatic attractions between between positive and negative “poles” of molecules
2 - 10 kcal/mol
1-6 kcal/mol
0.01 - 2 kcal/molIntermolecular forces of attraction
between molecules
London dispersion forces
Dipole-dipole interactions
Hydrogen bonding
Covalent bonds 70 - 200 kcal/molSingle, double, and triple covalent bonds
London Dispersion Forces• London dispersion forces are the attraction between
very temporary induced dipoles
Londondispersion.mov
London Dispersion Forces
– Exist between all atoms and molecules– In general, their strength increases as the
mass and number of electrons in a molecule increases
– Even though these forces are very weak, they contribute significantly to the attractive forces between large molecules because they act over large surface areas
Dipole-Dipole Interactions
• The electrostatic attraction between positive and negative dipoles– consider butane and acetone, compounds of
similar molecular weight
CH3CH2CH2CH3 CH3-C-CH3
O-
+Butane
(bp 0.5°C)Acetone(bp 58°C)
add electron densitymap of acetone
Hydrogen Bonds
• Hydrogen bond: a hydrogen covalently bonded to an atom of high electronegativity (O, N, F) is attracted to another O, N or F
• Affects bp, mp and solubility
H O
H
H
O
H
- +
hydrogenbond
hydrogenbond
- +
(a) (b) (c)
Liquids– When distances decrease so that almost all
molecules touch or almost touch, the gas condenses to a liquid
– The position of molecules in a liquid is random and there is irregular space between them into which other molecules can slide; this causes liquids to be fluid
– Surface tension can result
Evaporation/Condensation
– If a molecule is moving rapidly (has a high KE) and moving upward, it can escape the liquid and enter the gaseous space above it
– Eventually, the number of gaseous molecules will reach an equilibrium with the number of liquid molecules- the partial pressure of the vapor in equilibrium with the liquid: vapor pressurevapor pressure
– Boiling point:Boiling point: the temperature at which the vapor pressure of a liquid equals the atmospheric pressure
Evaporation/Condensation
Solids
– Upon cooling, molecules come so close together and attractive forces between them become so strong that random motion stops and a solid is formed : crystallization crystallization
– Can be crystalline or amorphous
crystallinestructure.mov
Types of Solids
Type Made up of Characteristics Examples
Ionic
Molecular
Polymeric
Network
Amorphous
ions in a crystallattice
high melting points NaCl, K2SO4
molecules ina crystal lattice
low melting points ice, aspirin
giant molecules;can be crystalline, semicrystalline, oramorphous
low melting pointsor cannot be melted;soft or hard
rubber, plastics, proteins
a very large numberof atoms connectedby covalent bonds
very hard; veryhigh melting orcannot be melted
diamond,quartz
randomly arrangedatoms or molecules
mostly soft, can bemade to flow, butno melting point
soot, tar, glass