chapter 5 states of matter gases, liquids, and solids denniston topping caret 6 th edition copyright...
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Chapter 5
States of Matter Gases, Liquids, and Solids
Denniston Topping Caret
6th Edition
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Changes in State
• Changes in state are considered to be physical changes
• During a change of physical state many other physical properties may also change
• This chapter focuses on the important differences in physical properties among• Gases• Liquids• Solids
Comparison of Physical Properties of Gases, Liquids, and Solids
5.1 The Gaseous State
Ideal Gas Concept
• Ideal gas - a model of the way that particles of a gas behave at the microscopic level
Kinetic Molecular Theory of Gases
1. Gases are made up of small atoms or molecules that are in constant, random motion
2. The distance of separation is very large compared to the size of the individual atoms or molecules o Gas is mostly empty space
3. All gas particles behave independently o No attractive or repulsive forces exist
between them
4. Gas particles collide with each other and with the walls of the container without losing energy o The energy is transferred from one atom or
molecule to another
5. The average kinetic energy of the atoms or molecules increases or decreases in proportion to absolute temperature o As temperature goes up, particle speed goes up
Kinetic Molecular Theory of Gases
Kinetic Molecular Theory of Gases
Explains the following statements:
• Gases are easily compressible – gas is mostly empty space, room for particles to be pushed together
• Gases will expand to fill any available volume – move freely with sufficient energy to overcome attractive forces
• Gases have low density – being mostly empty space; gases have low mass per unit volume
• Gases readily diffuse through each other – they are in continuous motion with paths readily available due to large space between adjacent particles
• Gases exert pressure on their containers – pressure results from collisions of gas particles with the container walls
• Gases behave most ideally at low pressure and high temperature
o Low pressure, average distance of separation is greatest, minimizing interactive forces
o High temperature, rapid motion overcomes interactive forces more easily
Measurement of Gases
• Gas laws involve the relationship between:o number of moles (n) of gaso volume (V)o temperature (T)o pressure (P)
• Pressure - force per unit area
• Gas pressure is a result of force exerted by the collision of particles with the walls of the container
http://www.7stones.com/Homepage/Publisher/Thermo1.html
Barometer• Measures atmospheric
pressureo Invented by Evangelista Torricelli
• Common units of pressureo atmosphere (atm)
o torr (in Torricelli’s honor)
o pascal (Pa) (in honor of Blaise Pascal)
• 1 atm is equal to:o 760 mmHgo 760 torro 76 cmHg
Gas Diffusion
Ammonia (17.0g/mol)
Ammonia diffused farther in same time, lighter moves faster
Hydrogen chloride (36.5g/mol)
Top:Start of expt
Bottom:End of expt
• Boyle’s law - volume of a gas varies inversely with the pressure exerted by the gas if the temperature and number of moles are held constant
• The product of pressure (P) and volume (V) is a constant
• Used to calculateoVolume resulting from pressure changeo Pressure resulting from volume change
PV = k1
Boyle’s Law
PiVi = PfVf
Application of Boyle’s Law• Gas occupies 10.0 L at 1.00 atm pressure• Product, PV = (10.0 L) (1.00 atm) = k1
• Double the pressure to 2.0 atm, decreases the volume to 5.0 Lo (2.0 atm)(Vx) = (10.0 L)(1.00 atm)o Vx = 5.0 L
Boyle’s Law Practice
1. A 5.0 L sample of a gas at 25oC and 3.0 atm is compressed at constant temperature to a volume of 1.0 L. What is the new pressure?
2. A 3.5 L sample of a gas at 1.0 atm is expanded at constant temperature until the pressure is 0.10 atm. What is the volume of the gas?
• It is possible to relate gas volume and temperature
• Charles’s law - volume of a gas varies directly with the absolute temperature (K) if pressure and number of moles of gas are constant
• Ratio of volume (V) and temperature (T) is a constant
2kT
V=
f
f
i
i
T
V
T
V =
Charles’s Law
Application of Charles’s Law• If a gas occupies 10.0 L at 273 K with V/T = k2
• Doubling temperature to 546 K, increasesvolume to 20.0 L 10.0 L / 273 K = Vf / 546 K
Practice with Charles’s Law
1. A 2.5 L sample of gas at 25oC is heated to
50oC at constant pressure. Will the volume
double?
2. What would be the volume?
3. What temperature would be required to
double the volume?
• If a sample of gas undergoes change involving volume, pressure, and temperature simultaneously, use the combined gas law
• Derived from a combination of Boyle’s law and Charles’s law
f
ff
i
ii
T
VP
T
VP=
Combined Gas Law
• Calculate the volume of N2 resulting when 0.100 L of the gas is heated from 300. K to 350. K at 1.00 atm
• What do we know?Pi = 1.00 atm Pf = 1.00 atmVi = 0.100 L Vf = ? L
Ti = 300. K Tf = 350. K
• Vf = ViTf / Ti this is valid as Pi = Pf
• Vf = (0.100 L)(350. K) / 300. K = 0.117 L• Note the decimal point in the temperature to indicate
significance
f
ff
i
ii
T
VP
T
VP=
Using the Combined Gas Law
Practice With the Combined Gas Law
Calculate the temperature when a 0.50 L sample of gas at 1.0 atm and 25oC is compressed to 0.05 L of gas at 12.6 atm.
• Avogadro’s Law - equal volumes of any ideal gas contain the same number of moles if measured under the same conditions of temperature and pressure
• Changes in conditions can be calculated by rewriting the equation
3kn
V=
f
f
i
i
n
V
n
V=
Avogadro’s Law
Using Avogadro’s Law
• If 5.50 mol of CO occupy 20.6 L, how many liters will 16.5 mol of CO occupy at the same temperature and pressure?
• What do we know?Vi = 20.6 L Vf = ? L
ni = 5.50 mol nf = 16.5 mol
Vf = Vinf / ni = (20.6 L)(16.5 mol) (5.50 mol) = 61.8 L CO
• Molar volume - the volume occupied by 1 mol of any gas
• STP – Standard Temperature and Pressureo T = 273 K (or 0oC)o P = 1 atm
• At STP the molar volume of any gas is 22.4 L
Molar Volume of a Gas
Gas Densities
• Density = mass / volume
• Calculate the density of 4.00 g HeoWhat is the mass of 1 mol of H2? 4.00 g
DensityHe = 4.00g / 22.4L
= 0.178 g/L at STP
• Combining: o Boyle’s law (relating volume and pressure)
o Charles’s law (relating volume and temperature)
oAvogadro’s law (relating volume to the number of moles)
gives the Ideal Gas Law
• R is a constant, ideal gas constant• R = 0.08206 L.Atm/mol.KIf units are P in atm, V in L, n in number of moles, T
in K
PV=nRT
The Ideal Gas Law
=⋅⋅
==atm 1
K 273)Kmol
atmL6mol(0.08201
P
nRTV 22.4 L
Calculating a Molar Volume
• Demonstrate molar volume of O2 gas
at STP
Practice Using the Ideal Gas Law
1. What is the volume of gas occupied by 5.0 g CH4 at 25oC and 1 atm?
2. What is the mass of N2 required to occupy 3.0 L at 100oC and 700 mmHg?
• Dalton’s law – a mixture of gases exerts a pressure that is the sum of the pressures that each gas would exert if it were present alone under the same conditions
• Total pressure of our atmosphere is equal to the sum of the pressures of N2 and O2
(principal components of air)
Pt=p1+p2+p3+...
22 ONair ppP +=
Dalton’s Law of Partial Pressures
Ideal Gases vs. Real Gases
• In reality there is no such thing as an ideal gaso It is a useful model to explain gas behavior
• Nonpolar gases behave more ideally than polar gases because attractive forces are present in polar gases
5.2 The Liquid State
• Liquids are practically incompressibleo Enables brake fluid to work in your car
• Viscosity - a measure of a liquid’s resistance to flowoA function of both attractive forces between
molecules and molecular geometryo Flow occurs because the molecules can easily
slide past each otheroGlycerol - example of a very viscous liquid
oViscosity decreases with increased temperature
Surface Tension• Surface tension - a measure of the attractive forces
exerted among molecules at the surface of a liquid
o Surface molecules are surrounded and attracted by fewer liquid molecules than those below
oNet attractive forces on surface molecules pull them downward
• Results in “beading”
• Surfactant - substance added which decreases the surface tension, for example – soap
Vapor Pressure of a Liquid
• Place water in a sealed containero Both liquid water and water vapor will exist in
the container
• How does this happen below the boiling point?o Temperature is too low for boiling conversion
• Kinetic theory - liquid molecules are in continuous motion, with their average kinetic energy directly proportional to the Kelvin temperature
energy + H2O(l) H2O(g)
Temperature Dependence of Liquid Vapor Pressure
• Average molecular kinetic energy increases as does temperature
• Some high energy molecules have sufficient energy to escape from the liquid phase
• Even at cold temperatures, some molecules can be converted
H2O(g) H2O(l) + energy
Movement From Gas Back to Liquid
• Molecules in the vapor phase can lose energy and be converted back to the liquid phase
• Evaporation - the process of conversion of liquid to gas at a temperature too low to boil
• Condensation - conversion of gas to the liquid state
Liquid Water in Equilibrium With Water Vapor
• When the rate of evaporation equals the rate of condensation, the system is at equilibrium
• Vapor pressure of a liquid - the pressure exerted by the vapor at equilibrium
Boiling Point• Boiling point - the temperature at which the vapor
pressure of the liquid becomes equal to the atmospheric pressure
• Normal boiling point - temperature at which the vapor pressure of the liquid is equal to 1 atm
• What happens when you go to a mountain where the atmospheric pressure is lower than 1 atm?o The boiling point lowers
• Boiling point is dependant on the intermolecular forceso Polar molecules have higher b.p. than nonpolar
molecules
Van der Waals Forces
• Physical properties of liquids are explained in
terms of their intermolecular forces• Van der Waals forces are intermolecular forces
having 2 subtypesoDipole-dipole interactions
Attractive forces between polar molecules
o London forces As electrons are in continuous motion, a nonpolar
molecule could have an instantaneous dipole
London Forces
• Exist between all molecules• The only attractive force between nonpolar
atoms or molecules• Electrons are in constant motion• Electrons can be, in an instant, arranged in
such a way that they have a dipole (Instantaneous dipole)
• The temporary dipole interacts with other temporary dipoles to cause attraction
Hydrogen Bonding
• Hydrogen bonding:
o not considered a Van der Waals force
o is a special type of dipole-dipole attraction
o is a very strong intermolecular attraction causing higher than expected b.p. and m.p.
• Requirement for hydrogen bonding:
omolecules have hydrogen directly bonded to O, N, or F
H-bonding in DNA
H-bonding in collagen
Examples of Hydrogen Bonding• Hydrogen bonding has an extremely important influence on the
behavior of many biological systems
• H2O
• NH3
• HF
5.3 The Solid State
• Particles highly organized, in a defined fashion
• Fixed shape and volume
• Properties of solids:o incompressibleom.p. depends on strength of attractive force
between particleso crystalline solid - regular repeating structureo amorphous solid - no organized structure
Types of Crystalline Solids
1. Ionic solids• held together by electrostatic forces• high m.p. and b.p.• hard and brittle• if dissolves in water, electrolytes• NaCl
2. Covalent solids• held together entirely by covalent bonds• high m.p. and b.p.• extremely hard• diamond
3.Molecular solids• molecules are held together with intermolecular forces• often soft• low m.p.• often volatile• ice
4.Metallic solids• metal atoms held together with metal bonds• metal bonds
o overlap of orbitals of metal atoms
o overlap causes regions of high electron density where electrons are extremely mobile - conducts electricity
Four Types of Crystalline Solids