States of Matter

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States of Matter

• Mr. Chan
• Northwestern University

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Day 6/15

• (30) Discuss HW/Labs
• (30) Quiz
• (30) States of Matter
• (30) Return Tests/Discuss
• (30) Gases
• Picture
• Lunch
• (30) Finish Gases
• (90) Labs

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Describing Gases according to Kinetic Theory of
Matter

• Tiny particles in all forms of matter are in
  constant motion
• Kinetic Theory Assumptions
• 1) gases are composed of small particles,
  insignificant volume, no attractive or repulsive
  forces
• 2) constant random motion
• 3) elastic collisions KE transferred without
  loss
• Gas Molecule Simulator

4
Gas Pressure

• Result of simultaneous collisions of billions of
  gas particles with an object
• Vacuum
• Empty space when no gas particles are present (no
  pressure)
• Force per Unit area
• Barometers
• Used to measure atmospheric pressure

5
SI units

• Millimeters Mercury (mmHg)
• Pascals (Pa), kilopascals (kPa)
• Atmospheres (atm)
• Atmospheric pressure
• Collisions of air molecules with objects
• Conversions
• 1 atm 760 mmHg 101.3 kPa
• Examples
• 1.5 atm gas convert to kPa and mmMg
• 190 mmHg convert into kPa and atm

6
Kinetic Energy distribution of molecules
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Kinetic Energy and Temperature

• Increase in average kinetic energy causes
  temperature of substance to rise, vice versa
• Absolute zero
• 0 K -273 C
• Motion of particles theoretically ceases
• Kelvin temperature directly proportional to
  average kinetic energy of particles

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Liquids

• Liquids flow, but more attracted to each other
  than to form a gas
• Liquids do not have enough energy to overcome IM
  (review Intermolecular) forces to become a gas
• Vaporization vs. Evaporation
• Both liquid to gas
• Vaporization liquid to gas
• Evaporation particles at surface
• Cooling processes
• Rubbing alcohol (on skin), acetone

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Evaporation in a closed container closed water
bottle how does the water get there?

• Vapor Pressure
• Force due to gas above liquid
• Increase temperature, increase vapor pressure
  explain why?
• Dynamic equilibrium
• Rates of evaporation and condensation are equal

10
Boiling Point

• Temperature where VP external pressure
• Normal boiling point at 101 kPa
• BP changes with changes in external pressure
• Vacuum pump demo?
• Higher altitudes
• Particles leaving liquid not as likely to
  encounter vapor particles
• Therefore, they need less energy to escape the
  liquid
• Denver water boils at 95 degrees
• Pressure cookers
• Water boils at temperatures well above 100
  degrees
• Temperature of boiling liquid plateaus
• Energy put in goes towards the boiling (overcome
  IM forces)

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Solids

• General Properties
• Particles organized, vibrating about fixed
  points, dense and incompressible
• Melting points/Freezing point
• Temperature where solid turns into a liquid
• Crystal Structures and Unit Cells
• Examples
• LAtomium

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Allotropes

• 2 or more different molecular forms of the same
  element, same physical state
• Examples
• Carbon Allotropes
• Diamond, graphite, bucky balls
• Amorphous solids
• Lack ordered internal structure
• Rubber, plastic, asphalt, glass
• Example Slime

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Changes of State

• Show phase diagram
• Relationships among 3 states of matter
  represented on a single graph (Pressure vs.
  Temperature)
• Equilibrium separates two regions
• Examine different temperature and pressure
  effects on boiling and melting points
• Triple point all three phases

14
Sublimation

• Solid directly to vapor without passing through
  liquid state
• Examples
• CO2, I2, ice sublimes to water vapor,
• air freshener demo?

15
Plasma (4th state of matter)

• Heating a gas to high temperatures
• KE separates molecules into atoms, then into ions
• Gaseous mixtures of electrons and positive ions
• Fluorescent lights, neon signs, northern lights
• Need lots of energy to create plasmas
• Plasma TVs

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Gases

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• Mr. Chan
• Northwestern University

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Describing Properties of Gases

• Recall Kinetic Theory for Gases
• Recall Gas simulator
• Large relative distance between molecules
• No attractive or repulsive forces exist
• Constant random motion, straight line path
• Average kinetic energy of particles directly
  proportional to Kelvin temperature of gas

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Factors that affect gas pressure

• Amount of gas
• Increase in gas, increase in gas pressure,
  removing gas - opposite
• Direct proportion
• Explain with KMT
• Increasing number of gas particles, number of
  collisions, pressure increases
• Sealed container example
• Examples? Tires, bballs, what happens when you
  leave the needle in?

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Factors that affect gas pressure

• Volume
• Decrease in volume, Increase in pressure
• Inverse proportion
• Explain with KMT
• Decrease in volume, less room for particles to
  move, more collisions with sides, increase
  pressure
• Examples syringes, plungers

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Gas Laws Boyles Law

• Pressure-Volume Relationship
• Fixed temperature and fixed amount of gas
• Mathematical Expression (use or think!)
• P1 X V1 P2 X V2
• Inverse proportion
• Demo Collapsing Can
• Animation
• Lee Marek 55 gallon drum
• Examples
• Balloon has 30 L of He, 100 kPa. What is volume
  of balloon when rises to altitude where pressure
  25kPa?
• Pressure of 2.50 L gas changes from 100 kPa to 40
  kPa. What is the new volume if temp is constant?

21
Factors that affect gas pressure

• Temperature
• Increase temperature, increase pressure
• Direct proportion
• Explain with KMT
• Increase temp, particles move faster, more
  collisions, increase pressure
• Examples car tires, bballs in winter,

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Gas Laws Charless Law

• Temperature-Volume Relationship
• Fixed pressure and amount of gas
• Mathematical Expression
• V1 / T1 V2 / T2
• Direct proportion
• Experiments led to determination of absolute zero
• Animation
• Examples
• Balloon 27 degrees Celsius has volume of 4.0 L,
  heated to temp of 57 degrees. What is new volume
  if pressure is constant?
• If sample of gas occupies 6.8 L at 327 degrees
  Celsius, what will its volume be at 27 degrees
  Celsius? (No change in Pressure)

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Gas Laws Gay-Lussacs Law

• Temperature-Pressure Relationship
• Fixed volume and amount of gas
• Mathematical Expression
• P1 / T1 P2 / T2
• Direct proportion
• Animation
• Examples
• Aerosol can pressure 100 kPa at room temp (27
  degrees). If can thrown into fire, what is
  internal pressure when temp reaches 927 celsius?
• A gas has pressure of 6.58 kPa at 540 K. What
  will pressure be at 210 K if volume does not
  change?

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Combined Gas Law

• Review three individual gas laws
• Put all three gas laws together into one
  expression
• Try to write equation
• (P1 X V1)/T1 (P2 X V2)/T2
• Also, taking each case separately thinking
  about gas law
• Examples
• The volume of a gas filled balloon is 30.0 L at
  40 degrees Celsius and 150 kPa pressure. What
  volume will the balloon have at standard
  temperature and pressure (STP)?
• A container with an initial volume of 1.0 L is
  occupied by a gas at a pressure of 150kPa at 25
  degrees Celsius. By changing the volume, the
  pressure of the gas increases to 600 kPa as the
  temperature is raised to 100 degrees Celsius.
  What is the new volume?

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Using the Ideal Gas Law

• Determining any of the variables associated with
  gases
• Also, we will now take into account the amount of
  gas
• PV/Tn constant (R)
• R 8.31 L kPA / mol K
• R 0.0821 L atm / mol K
• P x V n x R x T
• Tutorial
• Examples
• A cylinder is filled with a volume of 20.0 L of
  nitrogen gas at a pressure of 20,000 kPa at 27
  degrees Celsius. How many moles of N2 gas does
  the cylinder contain?
• When a rigid sphere containing 680 L of helium
  gas is heated from 300 K to 600 K, the pressure
  of the gas increases to 1800 kPa. How many moles
  of helium are in the sphere?

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Daltons Law of Partial Pressures

• Partial Pressure
• Each gas makes a contribution to the total
  pressure of a mixture
• Daltons Law
• Total pressure equals sum of the partial
  pressures
• Examples
• Air contains what gases?
• O2, N2, CO2, trace amounts
• What is partial pressure of O2 at 101.3 kPa if
  PN2 79.10kPa, PCO2 0.040 kPa, and Pothers
  0.94kPa?
• Determine the total pressure of a gas mixture
  that contains O2, N2, and He if partial pressures
  of the gases are PO2 20.0 kPa, PN2 46.7 kPa,
  and PHe 26.7 kPa.

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Avogadros Hypothesis

• Equal volumes of gases at the same temp and
  pressure contain equal numbers of particles.
• Easier to imagine since gas particles are so far
  apart
• Calculating volumes of gases at STP (Examples)
• Determine volume in liters, occupied by 0.202 mol
  of a gas at STP.
• Determine the volume in liters occupied by 14.0 g
  of nitrogen gas at STP.

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Deviations from Ideal Gases
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Differences between Ideal and Real Gases

• No gas behaves ideally at all temperatures and
  pressures
• Where are the exceptions?
• Gases vs. Liquids vs. Solids
• Attractive forces exist in liquids/solids
  (intermolecular forces)
• Volume
• As pressure increases, volume decreases
• Particles have real volume

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Grahams Law of Effusion

• Diffusion
• Molecules move toward areas of lower
  concentration until concentration is uniform
  throughout
• Effusion
• Gas escapes through tiny hole in container
• Gases with lower molar mass effuse faster than
  those with higher molar mass

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Grahams Law

• RateA/RateB MolarMassB/MolarMassA
• Practice
• Compare NH3 and HCl which effuses faster?
  Compare rates of effusion.

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Lab Changes of Physical State

• Objectives
• Observe behavior of substance during melting and
  freezing
• Graph heating and cooling curve
• Techniques/Notes
• Freezing point determination
• Use hot and room temp water
• Melting point determination
• Same
• Use clock or watch to estimate time
• Hypothesis
• What happens to temperature at melting point?
• If energy is still being added when going from
  solid to liquid, where does the energy go?
• Safety thermometer in test tube/rubber stopper
• Questions All except Do Research

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Lab Molar Volume of a Gas

• Objectives
• Determine Molar Volume (22.4) at STP through
  experiment.
• Use Combined Gas Law
• Techniques/Notes
• Equalizing Pressure
• Safety
• 6M HCl
• Questions All (if applicable)