UNIT 2 PHASES OF MATTER

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UNIT 2 PHASES OF MATTER

• Gas Phase Chap 13
• Pressure A force exerted over a unit of
  
• B. Measuring Pressure
• 1. Atmospheric Pressure the force of
  earths atmosphere on a unit of area
• 1 atmosphere is the pressure on earth at
• sea level STANDARD PRESSURE
• Atmospheric Pressure

1 unit
area.
1 unit
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2. SI unit of pressure kilopascals kPa

• 1 atm 101.3 kPa (Table A)
• Ex. Convert to kPa
• a. 2.0 atm _________kPa
• b. 0.5 atm _________kPa
• Ex. Convert to atm
• a. 405.2 kPa _________atm
• b. 20.3 kPa __________atm

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C. Kinetic Molecular Theory of Gases

• Behavior of Gases
• Expand to fill their containers
• Have no definite volume of their own
• Volume of gas Volume of container
• Low densities
• Exert pressure and have a temperature
• A theory needs to explain all these points.

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2. Assumptions of the Kinetic Molecular Theory

• Gases are made up of small particles (molecules)
  that are in constant random straight line motion.
  Temp. Ave. speed
• All collisions between molecules and between the
  walls of the container are elastic no energy
  lost!
• Pressure caused by collisions with walls
• c. The volume of individual molecules is zero.
• There is no attraction between molecules.
• Kinetic Molecular Theory Basic Concepts

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D. Ideal vs. Real Gases

• Ideal Gas a gas that perfectly fits the
  assumptions of the KMT. Its pressure,
  temperature and volume changes in an easily
  predictable way.
• Molecules have no volume
• Molecules dont attract can never be solid or
  liquid
• 2. Real Gases that most closely fit the KMT
• Hydrogen and Helium
• Any gas at High Temp. and Low Press.

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II. GAS LAWS

• A law is a mathematical equation.
• The gas laws relate the pressure, volume and
  temperature of a gas by equations.
• The gas laws were discovered in the 17th and 18th
  centuries in conjunction with steam engines
• A. Proportion a simple multiplication or
  division equality between variables.

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Direct Proportion

• As one variable inc. the other inc.
• A line with a positive slope and goes through the
  origin.
• Any two x and y values divided will be equal and
  the division equals the slope of the line.
• X1 X2 slope
• Y1 Y2

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2. Inverse Proportion

• As one variable increases the other decreases
• A downward hyperbola
• Any two x and y values multiplied will be equal.
• X1 x Y1 X2 x Y2

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B. Charles Law Temperature vs. Volume for an
Ideal Gas

• Measured the volume of a gas in a confined space
  with a movable top, at different temp.
• Temperature vs. Volume is a direct proportion if
  Kelvin temperature is used!
• V1 V2 Where T is
• T1 T2 in KELVIN!

gas laws
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Ex. A gas has a volume of 25.0ml at STP. What is
its volume if the temperature is changed to
100.oC, assuming constant pressure?
V1 V2 T1 T2
V1
25.0ml
25.0ml x..
T1
273K
273K 373K
V2
x
273x (25.0)(373)
T2
100oC
x 9325 34.2ml
373K
273
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C. Boyles Law Pressure vs. Volume for an Ideal
Gas

• Measured the volume of a gas in a confined space
  with a movable top, as pressure inc.
• Found, as press. inc. the volume of the gas dec.
  an inverse proportion!
• P1 x V1 P2 x V2

gas laws
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Ex. A gas has a volume of 40.0ml at STP. What
will its volume be if the pressure is increased
to 405kPa, assuming constant

• temperature?
• P1 101.3kPa
• V1 40.0ml
• P2 405kPa P1 x V1 P2 x V2
• V2 X 101.3kPa x 40.0ml 405kPa X
• 4052
  405X
• 405
  405
• X
  10.0ml

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D. Combined Gas Law

• P1 x V1 P2 x V2 T Temp. in K
• T1 T2 neither
  P or T
• kept
  constant
• If Temperature remains constant
• Remove Ts ? P1 X V1 P2 x V2
• If Pressure remains constant
• Remove Ps ? V1 V2
• T1 T2

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Ex. An ideal gas has a volume of 450ml at 10.oC
and 202.6kPa. What will its volume

• change to if the temperature increases to 360K
  and the pressure increases to 4.0atm?
• P1202.6kPa2.0atm
• V1450ml P1xV1 P2xV2
• T110oC283K T1 T2
• P24.0atm 2.0atm x 450ml 4.0atm X
• V2X 283K
  360K
• T2360K 1132X 324000
  
• 1132
  1132
• X
  290ml

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E. Gas Laws and the KMT

• Charles Law Why does V inc when T inc?
• Increase T causes particle velocity to inc.
• Particles strike container walls more often and
  with more energy.
• This causes walls to expand outward, inc V
• Boyles Law Why does V dec when P inc?
• The dec V causes the particles to be closer
  together.
• Particles strike container walls more often,
  increasing P

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II. Liquids and Solidschapter 14 p457 to 460
p471 to 473

• Liquids
• 1. Properties
• Shape No definite shape
• - particles are arranged randomly
• Volume Definite volume
• - particles are close together
• 2. KMT of Liquids

Matter States of Matter
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• B. Solids
• 1. Properties
• Shape Definite shape
• - Particles arranged in order
• Volume Definite volume
• - Particles are close together
• 2. KMT of Solids

Matter States of Matter
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C. Intermolecular Attractions

• Forces that hold the separate particles close
  together in the liquid and solid phases
  (condensed phases).
• Stronger Higher melting
  and
• intermolecular boiling points
• attractions Lower Vapor
• Pressure
• Vapor gas phase above a liquid or solid

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D. Vapor Pressure

• Evaporation the process in which particles at
  the surface of a liquid or solid leave to become
  a vapor. (Occurs below boiling point.)
• Temperature is the average speed of the
  particles, but some move faster fast enough to
  leave the surface.
• Vapor Pressure the pressure exerted by the gas
  phase of a substance above its liquid or solid
  phase.

Vapor Pressure
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E. Vapor Pressure vs. Temperature

• Vapor pressure can be thought of as the tendency
  of a particle to evaporate.
• This tendency does not depend upon amount of the
  liquid or solid but only on
• the temperature.
• As temp. inc.
• vapor pressure
• Low temp. increases.
  High temp.

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F. Boiling Point and Vapor Pressure

• Atmospheric pressure acts as a force to prevent
  particles from escaping
• atmospheric
  pressure
• vapor
  pressure
• intermolecular
  attractions
• As temperature inc., vapor pressure inc.
• Boiling point is the temperature at which vapor
  pressure atmospheric pressure.

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G. Boiling Point and Atmospheric Pressure

• Normal Boiling Point is the temperature at which
  a liquid will boil when the atmospheric pressure
  1atm 101.3kPa
• It is the temperature at which the vapor pressure
  1atm 101.3kPa
• The boiling pt. of a liquid will change if the
  atmospheric pressure is not 1atm
• ex. At what temperature will water boil at if
  the atmospheric pressure were 50 kPa?

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III. Phase Changes

• A. Heating Curve graph of temp. vs. time as a
  pure substances is heated through a phase change
  or changes. Ex.

Water
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Heating Curve for Water
KE
boiling
gas
PE
KE
liquid
melting
solid
PE
KE
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Heating Curve Movie
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B. Cooling Curve
gas
PE
KE
condensing
liquid
KE
PE
freezing
KE
solid
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C. Phase Changes
FUSION
VAPORIZATION
Boiling
Melting
SOLID LIQUID GAS
Condensing
Freezing
SUBLIMATION

• Fusion sol to liquid phase change
• Vaporization liquid to gas phase change
• Sublimation solid to gas phase change

ex. CO2(s) (Dry ice) and I2(s)
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D. Heats of Phase Changes

• Heat of fusion is the heat change required to
  melt 1 gram of a pure solid at its melting point
  temperature. Hf
• Heat lost in Heat gained 334 J/g
  freezing water in melting ice
• Heat of vaporization is the heat change required
  to boil 1 g of a pure gas at its boiling point
  temperature. Hv
• Heat lost in Heat gained
  2260 J/g condensing steam in boiling water

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E. Calculating heat changes during phase changes.

• During a phase change ?t0 so we cant use the
  equation q m x C x ?t.
• Since H is heat change for 1 gram,
• q m x H is heat change for m grams.
• ex. How much heat must be removed from 20.0g
  of steam at 100oC to condense it to liquid water
  at 100oC?

q m x H
x
q m Hv
x 20.0g x 2260J/g
20.0g
x 45,200J
2260J/g