Unit 4 - States & Changes of Matter

Gases

• Kinetic-Molecular Theory
  • Gases are a large number of constantly and randomly moving particles
  • Most of the volume of a gas is empty space
  • There is no force of attraction/repulsion between particles
  • All collisions are perfectly elastic
  • No energy is gained/loss during collisions
  • Kinetic Energy - The energy of movement [of particles]
  • Average kinetic energy is directly proportional to temperature
  • KE = (1/2)mv^2
• Ideal Gas - A theoretical gas composed of randomly moving particles that don’t interact with each other
  • Describes the behavior of most gases under common conditions
  • Fits the description of the Kinetic-Molecular Theory
  • Real gases deviating from this model under extreme conditions
• Properties of Gases
  • Compressibility
  • Change in pressure → change in volume
  • No fixed shape/volume
  • Expands to fit container
• Property Relationships
  • Pressure & Volume have an inverse relationship
  • Volume and Number of Atoms(# of moles) have a direct relationship
  • Pressure and Temperature have a direct relationship
  • Collision with container walls cause pressure
  • More/harder collisions = more pressure
  • Pressure = Force / Area
  • Volume and Temperature have a direct relationship
  • Pressure and Number of Atoms(# of moles) have a direct relationship
• Diffusion - Movement of particles from high concentration to low concentration
• Effusion - Movement of gas through a smaller opening into a larger volume
  • Graham’s Law - Rate of effusion is inversely proportional to the square root of molar mass

Liquids

• Kinetic energy of individual particles is similar to that of the intermolecular attraction between them
• Properties
  • More dense than gases
  • Have a fixed volume
  • Particles aren’t fixed in place
  • Can flow freely
  • Viscosity - The thickness / resistance to flow of a liquid
    • Directly related to intermolecular force
    • Directly related to size of molecules
    • Inversely related to temperature
  • Takes the shape of their container
  • Surface Tension - The tendency for a liquid to resist penetration
  • Directly related to intermolecular force
  • Surfactant - chemical compounds that can decrease surface tension
  • Incompressible
  • Can be used to transmit force, i.e hydraulics
  • Dissolvability - When a solid, liquid, or gas becomes integrated into a host liquid
  • Dissolved particles are dispersed evenly throughout the liquid
  • Miscible Liquids - liquids that are able to dissolve into each other
  • Immiscible Liquids - liquids that are not able to dissolve into each other
• Intermolecular Forces
  • Caused by uneven electron distribution
  • Affects interactions between particles
  • The stronger the force, the more kinetic energy particles need to move
  • Condensation - Gas → Liquid
  • Caused by intermolecular force > kinetic energy, meaning particles are pulled in towards each other
  • Evaporation/boiling - Liquid → Gas
  • *Evaporation is when small amounts of particles randomly gain enough energy, boiling is when the entire substance as a whole gains enough energy to change
  • Caused by kinetic energy > intermolecular force, meaning particles are pulled away from each other
  • Boiling point has a direct correlation w/ boiling points
    • Higher intermolecular force → higher boiling point
    • i.e ionic and polar covalent compounds have higher boiling points like non-polar covalent compounds
  • Freezing - Liquid → Solid
  • Caused by intermolecular force > kinetic energy
  • Melting - Solid → Liquid
  • Caused by kinetic energy > intermolecular force

Solids and Plasmas

• Solids
  • Properties
  • Low energy
  • Rigid structure
    • Molecules vibrates instead of move
  • Fixed shape & volume
  • Crystal - A solid whos components make up a highly ordered microscopic structure
  • Long Range Order - A property of crystals where their atomic particles show a periodic (recurring) pattern or shape
  • Lattice - A regular arrangement of atoms, molecules, etc
    • Incompressible
  • Amorphous Solids - Solids with particles arranged in non-uniform patterns
  • Can be caused by rapid cooling such that particles do not have time to fully arrange into a crystalline structure
  • Lack of long range order
  • Compressible
  • No definitive properties like boiling points due to changing pattern of molecules throughout
  • Molecules can shift & move past each other over time
• Plasmas
  • Properties
  • Composed of ionized (high-energy) particles
  • EXTREMELY HOT (high temperature)
  • Conducts electricity
  • Compressible
  • No definite volume/shape
  • Examples: Lightning, Stars, Auroras, Fluorescent Lights, Ion Thrusters, Arc Welders, Plasma Displays (plasma TVs), Plasma Balls, etc
  • Thermal Equilibrium - Temperature is equal to its surroundings
  • Plasma can be “cold“ when:
    • Their electrons break off from their nucleuses and move extremely quickly, dissipating the energy quickly
    • The energy in the electrons gets converted to light
    • Only a small percentage of the overall substance is ionized into a plasma
• Comparisons
  • Conduct Electricity - Plasmas always conduct electricity, only some solids do
  • Density - Plasmas have low density, solids have high density
  • Shape & Volume - Solids have fixed shape and volume, plasmas don’t
  • Kinetic Energy - Plasmas have high kinetic energy, solids have low kinetic energy
  • Composition - Plasmas are made of electrons and cations, solids are made of neutral particles or cation/anion pairs

Phase Changes

• Most of the phase changes are covered previously, so the only information here is going to be non-covered vocab and concepts
• Vapor Pressure - The pressure exerted by the gas in equilibrium with a liquid
  • Changes based on altitude; higher pressure → harder to boil
  • Higher vapor pressure → more likely to evaporate
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Properties of Water

• Water = H2O
  • Has a total of 8 valence electrons; stable
  • There are single bonds between the oxygen and each hydrogen, and two pairs of non-bonded electrons on the other side of the oxygen atom
  • “Tetrahedral“ electron-domain geometry
  • “bent“ molecular geometry
  • Bond Angle of 104.5*
• Properties
  • Oxygen --- Hydrogen bonds are highly polar → water is a polar molecule
  • Oxygen is partial negative, hydrogens are partial positive
  • Allows for hydrogen bonds
  • Strong solvent
    • Like dissolves like → Water mostly dissolves ionic and polar covalent compounds
    • Process of dissolving
      • Dissociation - Water breaks an ionic compound into cations and anions
      • Hydration - Water surrounds “broken apart“ substances
  • Adhesion/Cohesion - Intermolecular forces; polar “stick“ to polar
    • Adhesion is with other molecules, cohesion is with itself
  • Strong surface tension
  • High specific heat capacity
• Uses
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