Download NSCC Chem 121 chapter6

Spencer L. Seager
Michael R. Slabaugh
www.cengage.com/chemistry/seager
Chapter 6:
The States of Matter
PHYSICAL PROPERTIES OF MATTER
• All three states of matter have certain properties that help
distinguish between the states. Four of these properties are
density, shape, compressibility, and thermal expansion.
DENSITY
• Density is equal to the mass of a sample divided by the volume of
the same sample.
OTHER PHYSICAL PROPERTIES
• SHAPE
• The shape matter takes depends upon the physical state of the
matter.
• COMPRESSIBILITY
• Compressibility is the change in volume of a sample of matter
that results from a pressure change acting on the sample.
• THERMAL EXPANSION
• Thermal expansion is the change in volume of a sample of
matter resulting from a change in the temperature of the sample.
CHARACTERISTIC PROPERTIES OF THE
THREE STATES OF MATTER
PROBLEM 6.2, 6.6
KINETIC MOLECULAR THEORY OF MATTER
• The kinetic molecular theory of matter is a useful tool for
explaining the observed properties of matter in the three
different states of solid, liquid and gas.
• Postulate 1: Matter is made up of tiny particles called
molecules.
• Postulate 2: The particles of matter are in constant motion
and therefore possess kinetic energy.
• Postulate 3: The particles possess potential energy as a
result of repelling or attracting each other.
• Postulate 4: The average particle speed increases as the
temperature increases.
• Postulate 5: The particles transfer energy from one to
another during collisions in which no net energy is lost from
the system.
KINETIC ENERGY
• Kinetic energy is the energy a particle has as a result of being in
motion.
• Kinetic energy (KE) is calculated using the equation:
In this equation, m is the mass of a particle and v is its
velocity.
POTENTIAL ENERGY & FORCES
• POTENTIAL ENERGY
• Potential energy is the energy a particle has as a result of being
attracted to or repelled by other particles.
• COHESIVE FORCE
• A cohesive force is an attractive force between particles. It is
associated with potential energy.
• DISRUPTIVE FORCE
• A disruptive force results from particle motion. It is associated
with kinetic energy.
PROBLEM 6.9
THE SOLID STATE
• The solid state is characterized by a high density, a definite shape
that is independent of its container, a small compressibility, and a
very small thermal expansion.
THE LIQUID STATE
• The liquid state is characterized by a high density, an indefinite
shape that depends on the shape of its container, a small
compressibility, and a small thermal expansion.
THE GASEOUS STATE
• The gaseous state is characterized by a low density, an indefinite
shape that depends on the shape of its container, a large
compressibility, and a moderate thermal expansion.
A KINETIC MOLECULAR VIEW OF SOLIDS,
LIQUIDS, AND GASES
PROBLEM 6.12, 6.16
THE GAS LAWS
• The gas laws are
mathematical equations that
describe the behavior of
gases as they are mixed,
subjected to pressure or
temperature changes, or
allowed to diffuse.
• The pressure exerted on or
by a gas sample and the
temperature of the sample
are important quantities in
gas law calculations.
PRESSURE
• PRESSURE
• Pressure is defined as a force pushing on a unit area of surface
on which the force acts.
• In gas law calculations, pressure is often expressed in units
related to the measurement of atmospheric pressure.
• STANDARD ATMOSPHERE OF PRESSURE
• A pressure of one standard atmosphere is the pressure needed
to support a 760-mm (76.0-cm) column of mercury in a
barometer.
• ONE TORR OF PRESSURE
• One torr of pressure is the pressure needed to support a 1-mm
column of mercury in a barometer. A pressure of 760 torr is
equal to one standard atmosphere.
OFTEN-USED UNITS OF PRESSURE
TEMPERATURE
• The temperature of a gas sample is a measurement of the
average kinetic energy of the gas molecules in the sample.
• The Kelvin temperature scale is used in all gas law
calculations.
• ABSOLUTE ZERO
• A temperature of 0 K
is called absolute zero.
It is the temperature at
which gas molecules
have no kinetic energy
because all motion
stops. On the Celsius
scale, absolute zero is
equal to -273°C.
PRESSURE, TEMPERATURE, & VOLUME
RELATIONSHIPS FOR GASES
• Mathematical equations relating the pressure, temperature, and
volume of gases are called gas laws.
• All of the gas laws are named after the scientists who first
discovered them.
BOYLE'S LAW
• Boyle's law is a gas law that describes the pressure and volume
behavior of a gas sample that is maintained at constant
temperature.
• Mathematically, Boyle's law is written as follows:
or
In these equations, P is the pressure, V is the volume, and k
is an experimentally determined constant.
CHARLES'S LAW
• Charles's law is a gas law that describes the temperature and
volume behavior of a gas sample that is maintained at constant
pressure.
• Mathematically, Charles's law is written as follows:
or
In these equations, V is the volume, T is the temperature in
Kelvin, and k' is an experimentally determined constant.
THE COMBINED GAS LAW
• Boyle's law and Charles's law can be combined to give the
combined gas law that is written mathematically as follows:
In this equation, P, V and T have the same meaning as
before and k'' is another experimentally determined constant.
• The combined gas law can be
expressed in another useful form
where the subscript i refers to an
initial set of conditions and the
subscript f refers to a final set of
conditions for the same gas sample.
GAS LAW EXAMPLE
• A gas sample has a volume of 2.50 liters when it is at a temperature of
30.0°C and a pressure of 1.80 atm. What volume in liters will the sample
have if the pressure is increased to 3.00 atm, and the temperature is
increased to 100°C?
• Solution: The problem can be solved:
• using the combined gas law.
• by identifying the initial and final conditions.
• making sure all like quantities are in the same units.
• expressing the temperatures in Kelvin.
• Thus, we see that the combined gas law must be solved for Vf.
GAS LAW EXAMPLE (continued)
• The result is:
• Substitution of appropriate values gives:
AVOGADRO’S LAW
• Avogadro’s law states that equal volumes of gases measured
at the same temperature and pressure contain equal numbers
of molecules.
• STANDARD CONDITIONS
• STP = standard temperature and pressure
• 0°C (273 K)
• 1.00 atm
• MOLAR VOLUME AT STP
• 1 mole of any gas molecules
has a volume of 22.4 L at STP.
THE IDEAL GAS LAW
• The ideal gas law allows calculations to be done in which the amount of gas
varies as well as the temperature, pressure, and volume.
• Mathematically, the ideal gas law is written as follows:
PV= nRT
In this equation, P is the pressure of a gas sample, V is the
sample volume, T is the sample temperature in Kelvin, n is
the number of moles of gas in the sample, and R is a
constant called the universal gas constant. A commonlyused value for R is:
• In calculations, the quantities V, P, and T must be expressed in units that
match the units of R, liters (L), atm, and Kelvin, respectively.
IDEAL GAS LAW CALCULATIONS
• Example 1: A 2.50 mole sample of gas is confined in a 6.17 liter
tank at a temperature of 28.0°C. What is the pressure of the gas in
atm?
• Solution: The ideal gas equation is first solved for P:
The known quantities are then substituted into the equation, making
sure the units cancel properly to give units of atm in the answer:
IDEAL GAS LAW CALCULATIONS
(continued)
• Example 2: A 4.00 g sample of gas is found to exert a pressure of 1.71
atm when confined in a 3.60 L container at a temperature of 27°C.
What is the molecular weight of the gas in grams per mole?
• Solution:
• The molecular weight is equal to the sample mass in grams divided
by the number of moles in the sample.
• Because the sample mass is known, the molecular weight can be
determined by calculating the number of moles in the sample.
• The ideal gas equation is first solved for n:
• The known quantities are then substituted into the equation, making
sure units cancel properly to give the units of mol for the answer.
IDEAL GAS LAW CALCULATIONS
(continued)
• The units are seen to cancel properly to give the number of moles as
the answer. The molecular weight is calculated by dividing the
number of grams in the sample by the number of moles in the
sample:
IDEAL GASES vs. REAL GASES
• No ideal gases actually exist.
• If they did exist, they would behave exactly as predicted by the
gas laws at all temperatures and pressures.
• Real gases deviate from the behavior predicted by the gas
laws, but under normally encountered temperatures and
pressures, the deviations are small.
• Consequently, the gas laws can be used for real gases.
• Interparticle attractions make gases behave less ideally.
• The gas laws work best for gases made up of single atoms or
nonpolar molecules.
DALTON'S LAW OF PARTIAL PRESSURES
• According to Dalton's law, the total pressure exerted by a mixture
of gases is equal to the sum of the partial pressures of the gases
in the mixture.
PARTIAL PRESSURE
• The partial pressure of an individual gas of a mixture is the
pressure the gas would exert if it were alone in the container at the
same temperature as the mixture as shown in the following
illustration:
PROBLEM 6.18, 6.26, 6.36,
6.42, 6.50, 6.54, 6.56, 6.58
GRAHAM'S LAW
• Graham's law is a mathematical expression that relates the
rates of effusion or diffusion of two gases to the masses of
the molecules of the two gases.
• EFFUSION
• Effusion is a process in which a gas escapes from a
container through a small hole in the container.
• DIFFUSION
• Diffusion is a process that causes gases to spontaneously
mix when they are brought together.
MATHEMATICAL EXPRESSION OF
GRAHAM'S LAW
GRAHAM'S LAW CALCULATION EXAMPLE
• Compare the rates of effusion or diffusion for neon and krypton
gases.
• Solution: The molecular masses of neon and krypton are 20.18 u
and 83.80 u, respectively. These are the molecular weights of the
gases from the periodic table. Substitution into the Graham's law
equation gives the following:
Thus, the rate of Ne = (2.038) rate of Kr. Stated another way, neon
gas effuses or diffuses about twice as fast as krypton gas.
CHANGES IN STATE
• Changes in state are often accomplished by adding or removing
heat from a substance.
• Changes in state caused by adding heat to a substance are
classified as endothermic (heat in) processes.
• Changes in state caused by removing heat are classified as
exothermic (heat out) processes.
ENDOTHERMIC PROCESSES
• EVAPORATION OR VAPORIZATION
• Evaporation or vaporization is an endothermic process in which
a liquid is changed to a gas.
• SUBLIMATION
• Sublimation is an endothermic process in which a solid is
changed to a gas without first melting to a liquid.
• MELTING OR FUSION
• Melting or fusion is an endothermic process in which a solid is
changed to a liquid.
EXOTHERMIC PROCESSES
• LIQUEFACTION OR CONDENSATION
• Liquefaction or condensation is an exothermic process in which
a gas is changed to a liquid.
• DEPOSITION OR CONDENSATION
• Deposition or condensation is an exothermic process in which a
gas is changed into a solid.
• FREEZING OR CRYSTALLIZATION
• Freezing or crystallization is an exothermic process in which a
liquid is changed into a solid.
VAPOR PRESSURE
• Vapor pressure is the pressure exerted by a vapor that is in
equilibrium with its liquid.
BOILING POINT
• The boiling point of a liquid is the temperature at which the
vapor pressure of the liquid is equal to the prevailing
atmospheric pressure.
• The normal or standard boiling point is the temperature at
which the vapor pressure of a liquid is equal to 1 standard
atmosphere (760 torr).
VARIATION OF WATER
BOILING POINT WITH ELEVATION
SUBLIMATION AND MELTING
• Sublimation is the endothermic process in which a solid is
changed directly to a gas without first becoming a liquid.
ENERGY AND THE STATES OF MATTER
• At 760 torr, constant heat is applied until a 1 g sample of ice at
-20°C is converted to steam at 120°C.
• This is a five step process: (AB) heating ice to melting point, (BC)
melting ice, (CD) heating liquid to boiling point, (DE) boiling water,
and (EF) heating steam.
SPECIFIC HEAT
• The specific heat of a substance is the amount of heat required to
raise the temperature of exactly 1 g of a substance exactly 1°C.
HEATS OF FUSION & VAPORIZATION
• HEAT OF FUSION
• The heat of fusion of a substance is the amount of heat required
to melt exactly 1g of a solid substance at constant temperature.
• HEAT OF VAPORIZATION
• The heat of vaporization of a substance is the amount of heat
required to vaporize exactly 1g of a liquid substance at constant
temperature.
PROBLEM 6.64