2Common States of Matter GasesWhat do you know about gases?LiquidsWhat do you know about liquids?SolidsWhat do you know about solids?States of matter phet
3Kinetic Molecular Theory The KMT relates the kinetic energy of molecules to states of matter.Intro to KMT
4The Nature of Gases: Kinetic Molecular Theory (KMT) Kinetic Energy: what is it?Energy of a moving object: Ek = ½ mv2Assumptions of KMT as it applies to gasesGas particles…1. Have insignificant volume, (≈ 0)2. Are in constant, random motion3. Collisions are perfectly elastic4. Do not attract or repel one another5. Average Ek is proportional to absolute temp
6Gas Pressure Pressure = Force/Area: P = F/AGas pressure is the result of collision of gas particles with an object.Why is there no pressure in a vacuum?It is the sum of the force of collisions per unit area
7Atmospheric PressureAtmospheric pressure is due to the force of atmospheric gases colliding with objects and weight of atmospheric gases.
8Barometer Measures atmospheric pressure Invented by Alejandro TorricelliPatm presses down on the surface, forces Hg up into the tube
9Units of Pressure Pascal (SI unit) Pa Millimeters of Hg mmHg Atmosphere atmTorr torrConversion 25C: Know these!1 atm = 760 mmHg = 760 torr = kPa = 14.7 psi
10Converting Between Units of Pressure Convert a pressure of 385 mmHg to kilopascals (kPa)How would you do it?51.3 kPa
1213.2 The Nature of LiquidsBoth liquids and gases are fluids, i.e. they can flow
1313.2 The Nature of Liquids Key difference from gases: Molecules are close enough to have intermolecular forces of attractionThis is why liquids have a definite volumeBut not close enough to fix them in placeThis is why molecules of liquids can move past one another (flow)Condensed matter:Liquids and solids are known as condensed phases of matter
15Evaporation Vaporization: the conversion of a liquid to a gas or vapor Evaporation: vaporization occurring at the surface of a liquidDuring evaporation, molecules of liquid with sufficient KE “escape” in to the vapor phaseIn a closed container, some molecules that escaped re-enter into the liquid phase (condense)Eventually and equilibrium is reached where…The rate of evaporation equals the rate of condensationWhat would happen to the rate of evaporation when a liquid is heated? Why?
1613.2Vapor PressureVapor pressure is a measure of the force exerted by a gas above a liquid.States of matter phet
17Vapor PressureIn a closed container, as molecules escape into the vapor phase, pressure buildsThis is vapor pressureAt a certain pressure, the rate of vaporization equals the rate of condensationThis is an example of “dynamic equilibrium”Then vapor pressure is constant
18Vapor PressureDepends upon the liquidDepends upon temperature
19Vapor PressureDepends upon the liquidDepends upon temperature
20Boiling PointA liquid boils when the particles thoughout the liquid have enough KE to vaporizeThis occurs when the vapor pressure of the liquid equals the external pressure on the liquid (e.g. atmospheric pressure)This means that a liquid can boil at different temperatures, depending on the external pressure.
21Boiling Point & Normal Boiling Point Normal boiling point is the boiling temperature when atmospheric pressure (Patm) = 1 atmWhat is the normal BP for ethanol?What is the BP for ethanol at Patm = 600 torr?
2613.4 Changes of State Vaporization/Condensation Melting/Freezing Liquid ↔ GasEvaporationBoilingVapor vs. GasMelting/FreezingLiquid ↔ SolidSolidificationSublimation/DepositionSolid ↔ VaporI2 (s) → I2 (g)
27SublimationSolid VaporSublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature.DepositionVapor Solid
28Phase DiagramsShow pressure & temperature at which various states of matter exist for a given substancePhase equilibrium exists along each lineNormal m.p./b.p.Triple pointCritical pointNote negative slope for solid-liquidUnique to water
29Phase DiagramsA phase diagram is a graph that gives the conditions of temperature and pressure at which a substance exists as solid, liquid, and gas (vapor).Lines represent pressures and temperatures at which two phases are in equilibrium