Chapter 6:The States of Matter

Spencer L. SeagerMichael R. Slabaugh

www.cengage.com/chemistry/seager

Jennifer P. Harris

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.

A KINETIC MOLECULAR VIEW OF SOLIDS, LIQUIDS, AND GASES

DENSITY• Density is equal to the mass of a sample divided by the volume

of the same sample.

High density high – med density low density

volume

massdensity

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.

Effusion and Diffusion

• 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.

CHARACTERISTIC PROPERTIES OF THE THREE STATES OF MATTER

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.

2

mvKE

2

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.

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.

Add Heat Give off Heat

ENDOTHERMIC PROCESSESHEAT IS ADDED

• 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 PROCESSESHEAT IS REMOVED

• CONDENSATION• Condensation is an exothermic process in which a gas is

changed to a liquid.

• DEPOSITION• Deposition is an exothermic process in which a gas is

changed into a solid.

• FREEZING• Freezing 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.

High vapor pressure = low boiling point

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.

HEATS OF FUSION & VAPORIZATION

• 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.

• 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.

GASES

• Intermolecular forces are minimal

• Move independent of each other

• High velocity – move in random motion

• Higher kinetic energy than liquids or solids

• Volume occupied is negligible compared to

volume of container

PRESSURE

• PRESSURE• Pressure is the force pushing on a unit

area of surface on which the force acts.

• 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 atwhich gas moleculeshave no kinetic energy because all motion stops. On the Celsiusscale, absolute zero isequal to -273°C.

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

R = K mol

atm L0.0821

P Pressure atm

V Volume Liters

n Number of moles moles

T Temperature Kelvin

R Universal gas constant

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.

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.

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:

V

nRTP

atm 0.10L 17.6

K 301K mol

atm L0.0821mol 2.50

P

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.

RT

PVn

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:

mol 0.250

K 300K mol

atm L0821.0

L 60.3atm 1.71n

mol

g0.16

mol 0.250

g 4.00mw

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.

VARIATION OF WATER BOILING POINT WITH CHANGE IN PRESSURE

PV = nRT (Assuming V and n are equal)

• at high elevation P decreases, T decreases• Pressure cooker P increases, T increases (cooks faster)

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.

'k'T

PV

f

ff

i

ii

T

VP

T

VP

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:

fi

fiif PT

TVPV

liters 85.1

atm 00.3K 303

K 373liters 50.2atm 80.1Vf

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:

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.

Zn(s) + NH4NO3(s) → N2(g) + 2 H2O(g)  + ZnO(s)

gases individualtotal PP

P total = PN2 + PH2O