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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