Presentation on theme: "The Kinetic Molecular Theory"— Presentation transcript:
1The Kinetic Molecular Theory Basic AssumptionsParticle SizeGas particles have no volume (pin point particles)The space between particles is extremely large compared to the volume of the particles. Due to this distance, there is no significant attractive or repulsive force acting on the particles.
2The Kinetic Molecular Theory Basic AssumptionParticle MotionGas particles are in constant random motion.Collisions between particles are elastic (Energy can be transferred from one particle to another during a collision, but no energy is lost when particles collide)
3Basic Assumptions Particle Energy The mass and velocity of a particle determine the kinetic energy of a particleTemperature is a measure of the average kinetic energy of particles in a sample.
4The Kinetic Molecular Theory Mass/Velocity Relationship QuestionsCondition #1:Two particles (one heavy and one light) traveling at the same velocity.Which exhibits the greatest kinetic energy?Condition #2:Two particles of the same size traveling at different velocities (fast and slow).
5Explaining the Behavior of Gases PropertiesLow Density (pinpoint mass/volume of empty space)Random MotionBehaviorsCompressionGases can be compressed due to the large space that exists between particlesGases expand to fill their containers due to constant random motion
6Explaining the Behavior of Gases PropertiesNo attractive or repulsive forces acting on particlesParticles exhibit constant random motionBehaviorsParticles can flow easily past each other in a process called diffusion. The rate of diffusion is dependent on the mass of the particles.Question: Based on this equation which particles diffuse faster, heavy or light particles?
7Explaining the Behavior of Gases PropertyParticles exhibit constant random motionBehaviorEffusion (similar to diffusion, where particles escape through a tiny opening)Graham’s Law of EffusionRate of effusion
8Gas Pressure An important property of any gas is its pressure A linear momentum of the gas moleculesPressure is defined as force per unit areaGas particles exert pressure when they collide with the walls of their containerThe less mass, the less pressure it exerts
9Gas Pressure (Continued) Temperature, volume and number of moles affect the pressure that a gas exertsThe Earth is surrounded by an atmosphere that extends into space for hundreds of kilometers.The particles in air move in every direction which exerts pressure in all of these directions; this is known as atmospheric pressureAir Pressure varies at different points on earth
10Measuring Gas Pressure Evangelista Torricelli ( ) was the first to demonstrate that air exertedHe designed experiments in order to test his theories about liquid and densityHe invented a barometer: an instrument used to measure atmospheric pressure
12Units of Pressure The SI unit of pressure is called the pascal (Pa) The pressures measured by barometers and monometers can be reported in:Millimeters of mercury (mm Hg)Also the Torr, which is named after TorricelliAir Pressure is often reported in a unit called an atmosphere (atm)1 atm= 760 mm Hg760 torr101.3 kPa (kilopascals)14.7 psi (pounds per square inch)
13Dalton’s Law of Partial Pressure Dalton’s Law explains that the totally pressure is equal to the sum of all the pressures of the partsThis is only true for ideal gases, but the error is small for real gasesPressureTotal = Pressure1 + Pressure2 + PressurenThe portion of the total pressure contributed by a single gas is called its partial pressurePartial pressure of a gas depends onNumber of moles of gasSize of the containertemperature
15Forceholds all matter together. The force in a molecule that is between atoms is a chemical or intramolecular force. The force between molecules is called a physical or intermolecular force.
16Dipole-dipole Forcesare attractive forces between the positive end of one polar molecule and the negative end of another polar molecule. Dipole-dipole forces have strengths that range from 5 kJ to 20 kJ per mole. They are much weaker than ionic or covalent bonds and have a significant effect only when the molecules involved are close together.
17Figure: two arrangements of polar iodine monochloride (ICl) molecules that give rise to dipole-dipole attractions.
18Hydrogen Bondsspecial type of dipole-dipole attractionDefinition: a dipole-dipole attraction that occurs between molecules containing a hydrogen atom bonded to a small, highly electronegative atom with at least one lone electron pair.only form to fluorine, oxygen, or nitrogen atoms.REASON: they are electronegative enough to cause a large partial positive charge on the hydrogen atom, but small enough that the lone pairs of electrons can come close to hydrogen atoms.
19Hydrogen Bonds in a water molecule: Water has two hydrogen atoms and one oxygen atom. Two molecules of water can form a hydrogen bond between them. The oxygen of one water molecule has two lone pairs of electrons, each of which can form a hydrogen bond with hydrogen on two other water molecules.
20Density & CompressionDensity- Density is a measurement of the mass per unit volumeCompression- This unit of measure expresses the degree of firmness or softnessLiquids can be compressed but the change in volume for liquids is much smaller because liquid particles are already tightly packedLiquids are much denser than gases
21Fluidity Fluidity- The ability to flow A liquid can diffuse through another liquidLiquids diffuse more slowly than gases even at the same tempLiquids are less fluid than gases
22Viscosity Viscosity- The measure of the resistance of a liquid to flow Viscosity of a liquid is determined by the type of intermolecular forces, the shape of the particles, and temperatureThe stronger the forces, the higher the viscosityViscosity decreases with temperatureThe added energy from a higher temperature makes it easier for the molecules to overcome the intermolecular forces that keep the molecules from flowingHigher viscosity with higher molecular mass
23Surface TensionSurface Tension- The measure of the inward pull by particles in the interior if the liquidFor the surface area to increase particles from the interior must move to the surfaceThe stronger the attractions between particles, the greater the surface tensionSurfactants- Compounds that lower the surface tension of water, also referred to as surface agentsWater has a high surface tension because its molecules can form multiple hydrogen bonds
24Capillary ActionCapillary Action- The movement of a liquid along the surface of a solid caused by the attraction of molecules of the liquid to the molecules of the solid (adhesion)Molecules of water are naturally attracted to each other and form temporary hydrogen bonds with each other (cohesion); their attraction for each other on the surface of a liquid, for example, gives rise to surface tensionResults in the elevation or depression of liquids in capillaries (small narrow tubes)
25Density of Solids Except water There is about a 10% difference in density between the solid and liquid states of most substancesIn general, the particles in solids are more closely packed than those in liquidsMost solids are more dense than most liquidsExcept waterthe water molecules in ice are less closely packed together than in liquid water
26Crystalline SolidsA solid whose atoms, ions, or molecules are arranged in an orderly, geometric, three-dimensional structureCrystals -- The individual pieces of a crystalline solidUnit Cell -- the smallest arrangement of connected points that can be repeated in 3 dimensions to form the latticeThe shape of a crystalline solid is determined by the type of unit cell from which its lattice is builtCrystal shapes differ because the surfaces of unit cells do not always meet at right angles and the edges of the faces vary in length
27Molecular Solids The molecules are held together by dispersion forces, ex: table sugarThe molecules are held together by dispersion forces,dipole - dipole forces or hydrogen bondsMost are not solid at room temperatureMolecular compounds are solids at room temperature because of their large molar massBecause they have no ions, molecular solids are poor conductors of heat and electricityFairly soft and have low to moderately high melting points
28Covalent Network of Solids ex: quartz and diamondAtoms that can form multiple covalent bonds are able to form covalent network solidsVery high melting pointsUsually have poor conductivity
29Ionic Solidsex: table saltEach ion is surrounded by ions of opposite chargeThe type of ions and the ratio of ions determine the structure of the lattice and the shape of the crystalThere is a network of attractions that extends throughout an ionic crystalThis gives these compounds their high melting points and hardnessIonic crystals are strong but brittle
30Metallic Solids Strength varies by the physical property Consists of positive metal ions surrounded mobile electronsStrength varies by the physical propertyMobile electrons make metals malleable and ductileThey also make metals good conductors of electricity and heatWhen force is applied to a metal, electrons shift and keep the metal ions bonded in their new positionsAll metallic elements can form a metallic solid
31Amorphous SolidsA solid in which there is no long range order of the positions of the atomsex: glass and rubberHas no shapeAny liquid can be made into an amorphous solid if given a sufficiently high cooling rateCooling reduces molecular mobilityAn amorphous solid often forms when a molten material cools too quickly to allow enough crystals to formNot all particles are arranged in specific order
32Endothermic Processes Endothermic- A chemical reaction in which a greater amount of energy is required to break the existing bonds in the reactants than is released when the new bonds form in the product molecules
33MeltingThe amount of energy required to melt one mole of a solid depends on the strength of the forces keeping the particles together in the solidThe melting point of a crystalline solid is the temperature at which the forces holding its crystal lattice together are broken and it becomes a liquid
34Vaporization vs. Evaporation Vaporization is the process by which a liquid changes to a gas or a vaporEvaporation is when vaporization occurs only at the surface of a liquid
35BoilingThe temperature at which the vapor pressure of a liquid equals the external or atmospheric pressure is called the boiling point
36Process of BoilingMolecules throughout the liquid have energy to vaporizeBubbles of vapor collect below the surface of the liquid and rise to the surface
37SublimationSublimation is the process by which a solid changes directly to a gas without first becoming a liquid
38Exothermic ChangesExothermic- A chemical reaction in which more energy is released than is required to break bonds in the initial reactionature=related
39CondensationThe energy-releasing process by which a gas or vapor becomes a liquidCondensation is the reverse of vaporizationDifferent causes of the condensation of water vapor in which all involve a transfer of energy
40CondensationThe vapor molecules can come in contact with a cold surface such as the outside of a glass containing ice waterHeat from the vapor molecules is transferred to the glass as the water vapor condensesThe water vapor that condenses on blades of grass or the car forms liquid droplets called dew
41CondensationWhen a layer of air near the ground cools, water vapor in the air condenses and forms fogClouds form when layers of air high above the surface of Earth cool
42DepositionThe energy-releasing process by which a substance changes from a gas or vapor to a solid without first becoming a liquidDeposition is the reverse of sublimationWhen water vapor comes in contact with a cold window in winter, it forms a solid deposit on the window called frost
43Freezing Freezing is the reverse of melting The freezing point is the temperature at which a liquid is converted into a crystalline solid
44Phase DiagramsTwo variables control the phase of a substance: temperature and pressurePhase Diagram- a graph of pressure versus temperature that shows which phase substance exists under different conditions of temperature and pressure
45Phase DiagramsTriple Point- the point on a phase diagram representing the temperature and pressure at which three phases of a substance (solid, liquid, and gas) can coexistCritical Point- indicates the critical pressure and critical temperature above which water can not exist as a liquid