Chapter 6 The States of Matter

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Chapter 6: The States of
Matter
Suggested Problems:
States of Matter
• ______
– Definite volume and shape
• ______
– Definite volume but not
shape
• Takes the shape of its
container
• _______
– No definite volume or shape
• Will not only take the shape
of its container it will fill it
completely
Solids
• A __________ state of matter
• Atoms (or molecules) are “touching”
• Strongest intermolecular forces
– Hold atoms (or molecules or ions, etc.) rigidly
in a 3D crystalline lattice
Liquids
• Also a __________ state of matter
• Atoms (or molecules) are “touching”
• Intermolecular forces hold atoms (or
molecules) in contact, but not rigidly in
place…molecules can slide past each
other
Gases
• Virtually ___ intermolecular forces
• Gaseous molecules (etc.) comprise a very small
percent of the sample volume
• Gaseous molecules are in constant random
motion…the velocity is related to temperature
• Molecules collide with walls of container and
with each other and bounce off with no loss of
energy
Properties of Gases
• Gases are the best understood state of
matter, because we ignore intermolecular
forces
• The volume a gas sample occupies is a
function of three variables:
– ___________
– ___________
– ___________
Pressure
• Pressure is force per unit area
• Units of pressure:
– Pounds per square inch
– Torr or mmHg
– Atmosphere
1 atm = 760 torr = 760 mmHg = 14.7 psi
Measuring Pressure: Barometer
gravity pulling down
air pushing down
Pressure Conversion Example
• The gauge on an oxygen gas cylinder
reads 1272 psi. Express this in atm and
torr. (1 atm=14.7 psi)
Volume of a Gas
• Imagine a fixed amount of air
at a given temperature and
pressure in a balloon
• What will happen to the
volume if we add more air?
Volume of a Gas
• Imagine a fixed amount of air
at a given temperature and
pressure in a balloon
• What will happen to the
volume if we squeeze the
balloon (increase pressure)?
Volume of a Gas
• Imagine a fixed amount of air
at a given temperature and
pressure in a balloon
• What will happen to the
volume if we increase the
temperature?
The Combined Gas Law
P1V1 P2 V2

n1T1 n 2 T2
• P is pressure
• V is volume
• T is ________
temperature
• n is number of moles
The Empirical Gas Laws
• Boyle’s Law
– Volume is inversely proportional to pressure
(constant n and T)
• Charles’s Law
– Volume is directly proportional to the Kelvin
temperature (constant n and P)
• Avogadro’s Law
– The volume of a gas is directly proportional to the
number of gas moles (constant T and P)
Boyle’s Law: Example
• 15 liters of argon is collected at an initial
pressure of 1.05 atm. If the gas is
compressed to a new pressure of 1510
torr, what is the new volume?
Charles’s Law: Example
• The temperature of 35.6 mL of neon is
increased from –35.4ºC to 75.2ºC. What is
the new volume?
Combining Boyle’s and
Charles's Laws
• A bubble of air having a volume of 75.0
mL is released from 35 feet under the sea
(where the pressure is 2.07 atm and the
temperature is 18 ºC). What will the new
volume be at the surface, where P=0.967
atm and T=23 ºC?
The Ideal Gas Law
• Combines the elements of the ________ gas
laws
P1V1 P2 V2

 constant R
n1T1 n 2T2
P V  nRT
L  atm
R  0.0821
mol K
Standard Conditions
• STP = standard temperature and pressure
T = _____ K (_____ ºC)
P = _____ atm = ____ torr
Example
• What volume will 2.0 grams of helium
occupy at a temperature of 290K and a
pressure of 800 torr?
Which Gas Law to Use?
• Use the combined gas law when the
problem describes two sets of conditions
– the pressure and/or temperature changes
• Use the ideal gas law when there are a
single set of conditions
Dalton’s Law of Partial
Pressures
• The ______ pressure of a gaseous
mixture is the sum of the partial pressures
Nitrogen
0.75 atm
Nitrogen
0.75
atm
Empty
container
Oxygen
0.25 atm
Ptotal =
Oxygen
0.25 atm
Graham’s Law
• __________ is net movement of a gas from an
area of high concentration (pressure) to an area of
lower concentration
• __________ is the movement of a gas through a
pinhole
• Both Diffusion and Effusion follow Graham’s Law
Rate1
MW2

Rate2
MW1
Rate is an amount per time
Graham’s Law Example
• Oxygen Molecules weigh 16 times as
much as hydrogen molecules. Which
molecule will diffuse faster and how much
faster?
Changes of State
Gas
freeze
Liquid
melt
What do all of these changes
in state have in common?
Solid
Energy
• Energy is the ability to do work
– Kinetic Energy: energy due to motion
– _________ Energy: stored energy
– Heat Energy: the sum of the kinetic and
potential energies of molecules in a sample
Energy and Its Units
• calorie (cal): is the amount of heat needed
to raise the temperature of 1 gram of water
o
by 1 degree Celsius at 15 C
• kilocalorie = 1000 cal
• A food Calorie = 1000 cal
• Joules (J): are the metric unit of energy
1 cal = 4.184 J
Energy Conversion Example
• A candy bar has 350 Calories. How many
joules does one candy bar contain?
Heat and Temperature
• __________: is a measurement of the
average kinetic energy of the molecules in
a sample
– ___ is measured in degrees with a
thermometer
• _______: is the sum of the kinetic (and
potential) energies in a sample
– _____ is measured in calories with a
calorimeter
Calorimeters
Bomb Calorimeter
Coffee Cup Calorimeter
Specific Heat
• Specific heat (SH) is the amount of heat needed
to raise the temperature of 1 gram of material by
one degree Celsius
q  (mass)(SH)(T )
q
SH 
mass  T
q  heat
T  (TF  TI )
Specific Heat Example
• A 10.0 gram sample of copper at 25 ºC
has a final temperature of 100 ºC when
289 J of heat are added. What is the
specific heat of copper? (SH of liq water =
o
4.18 J/g C)
Distribution of Energy
• In a sample of material, the kinetic energies of the
molecules follow a Boltzman Distribution:
# Molecules
Average KE
1
KE  mv2
2
m  mass
v  velocit y
Kinetic Energy
Kinetic Energy Distribution
# Molecules
Tlow
Thigh
Kinetic Energy
Changes of State
Gas
freeze
Liquid
melt
Solid
Vaporization
• The most energetic molecules in a liquid
have sufficient kinetic energy to escape
into the ____ phase
• Once the molecules are free as gases,
they exert a pressure
– This is called the ______ pressure
• How does vapor pressure depend on
temperature?
Vapor Pressure of Water and
Ethanol
1000
900
800
Vapor Pressure (Torr)
700
vapor
pressure of
ethanol
600
500
400
vapor
pressure of
water
300
200
100
0
0
20
40
60
Temperature ( oCelcius)
80
100
Boiling Point
• The boiling point of a liquid is the
temperature where the vapor pressure
equals the ambient pressure.
• The _______ boiling point of a liquid is the
temperature where the vapor pressure
equals 760 torr.
• How does boiling point depend on
pressure?
Changes of State
Gas
freeze
Liquid
melt
What do all of these changes
in state have in common?
Solid
Freezing/Melting Point
• The melting point of a substance is the
temperature at which a crystalline solid
changes to a liquid.
• What is the difference between melting
point and freezing point?
Energy Changes and Changes
of State
• Imagine recording the temperature of an 18
gram (i.e., 1.0 mole) sample of ice at -40ºC as
heat is added
heat added, kJ
0.0
1.5
7.5
15.0
55.7
56.5
temperature
-40
0
0
100
100
120
No T
No T
Heating Curve for 1 Mole of Water
120
100
Water is boiling:
Heat of vaporization
40.7 kJ/mol
Temp (oC)
80
60
40
20
Ice is melting:
Heat of fusion
6.02 kJ/mol
0
-20
-40
0
10
20
30
kilojoules of heat added
40
50
60
Molar Heat of Fusion
 Hºfus is the heat required to convert one
mole of solid to a liquid at at its normal
melting point
 Hºfus represents the energy needed to
break down intermolecular forces and
allow molecules to slide around the liquid
phase
Molar Heat of Vaporization
 H°vap is the heat required to convert one
mole of liquid to a gas at at its normal
boiling point
 H°vap represents the energy needed to
break intermolecular forces and allow
molecules to escape into the gas phase
Putting it all Together
• How much heat is required to convert an 18 gram
piece of ice at -40 oC to steam at 120 oC?
Heating Curve for 1 Mole of Water
120
D
100
Heat of vaporization
40.7 kJ/mol
Temp (oC)
80
C
60
40
q = m(SH)(T)
20
B
Heat of fusion
6.02 kJ/mol
0
A
-20
E
o
SH ice = 2.1 J/g C
o
SH liq = 4.18 J/g C
o
SH gas = 2.0 J/g C
-40
0
10
20
30
kilojoules of heat added
40
50
60
Question
• Explain why orange growers spray their
trees with water when there is a threat of
freezing temperatures.
Question
• Why does steam at 100ºC cause more
severe burns than water at the same
temperature?

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