2Ideal Gas ConceptA model of the way that particles behave at the microscopic levelInvolves the relationship between pressure (P), volume (V), temperature (T) and number of moles of gas (n).Pressure is force per unit area.
3Atmospheric pressureAtmospheric pressure measured with a barometer has a unit of mmHg (millimeters of mercury)A commonly used unit of measurement is the atmosphere1 atm = 760 mmHg1 mm Hg = 1 torr1 atm =1.01 x 105 pascals
4Kinetic Molecular Theory of Gases Gases are easily compressible.Gases will expand to fill any available volume.Gases have low density.Gases readily diffuse through each other simply because they are in continuous motion.Gases exert pressure on their containers.Gases behave most ideally at low pressures and high temperatures.
5Boyle’s LawPiVi=PfVfThe volume of a gas varies inversely with the pressure exerted by the gas if the number of moles and temperature of gas are held constant
6Charles’s LawTemperature must be converted to Kelvin before Charles’s law is applied.Watch for the question requesting the “difference” in temperature or volume.
7Combined Gas LawOften a sample of gas undergoes change involving volume, pressure, and temperature simultaneously.
8Avogadro’s LawEqual volumes of any ideal gas contain the same number of moles if measured under the same conditions of temperature and pressure.
9Molar Volume of a Gas The volume occupied by 1 mol of gas At STP (standard temperature and pressure) the molar volume of any gas is 22.4LT = 273 KP = 1 atm
10Ideal Gas LawCombining Boyle’s, Charles’s and Avogadro’s Law into a single expressionpV = nRTP in atmospheresV in litersn in number of molesT in Kelvin
11Dalton’s Law of Partial Pressures A mixture of gases exerts a pressure that is the sum of the pressures that each gas would exert if it were present alone under the same conditions.
12The Liquid State Compressibility: Liquids are practically incompressibleThe application of many atmospheres of pressure does not significantly decrease the volumeThis is why liquids are used in the brake lines of an automobile and in hydraulicsInstead of compressing the fluid, it transmits it directly to the brake pads, forklift, etc.
13Viscosity Measure of resistance to flow A function of both attractive forces between molecules and molecular geometryMolecules with complex structures resist sliding smoothly past each otherPolar molecules tend to have higher viscosityGlycerol is very viscous, gasoline is not
14Surface tensionMeasure of the attractive forces exerted among moleculesThe net attractive forces on the surface molecules pulls them downward into the body of the liquidResponsible for the spherical shape of drops of liquidSurfactants can be added to liquid to decrease surface tension
15IRDSInfant respiratory distress syndrome is the developmental insufficiency of surfactant production and structural immaturity in the lungsThe surfactant helps prevent collapse of the terminal air-spaces throughout the normal cycle of inhalation and exhalationOne of the most commonly used surfactants is Survanta, derived from cow lungs
16Vapor Pressure of a Liquid Related to evaporation, condensation and boiling pointWhen temperature is too low for a phase change, that’s just the average kinetic energyEvaporation happens when pockets of high-energy molecules possess sufficient energy to escape from the bulk liquid
18CondensationEvaporation is the conversion of liquid to a gas at a temperature too low to boil.Condensation is the conversion of a gas to the liquid state.Vapor pressure is the pressure exerted by the vapor at equilibrium between rates of evaporation and condensation.
19Normal Boiling pointThe boiling point of a liquid is defined as the temperature at which the vapor pressure of the liquid become equal to the atmospheric pressureNormal boiling point is the temperature when vapor pressure of the liquid is equal to 1 atmTherefore at high altitudes (less atmospheric pressure), boiling points are lower.Polar liquids have higher boiling points than nonpolar liquids.
20Van der waals forcesThe dipole-dipole interactions of polar molecules decreases vapor pressure and increases boiling pointIn nonpolar liquids, instantaneous dipoles are created for short periods of time, due to the constant movement of electronsThe interaction of these instantaneous dipoles is called London forces.Dipole-dipole and London forces are collectively called Van der Waals forces
21Hydrogen BondingWhen Van der Waals forces are not strong enough to account for high boiling pointsMolecules where an hydrogen atom is bonded to a small, highly electronegative atom: N, O, or FA large dipole is created
22More on Hydrogen Bonding Boiling points increase as the electronegativity of the element bonded to hydrogen increasesBoiling points from least to greatest:Water > hydrogen fluoride > ammonia > methane
23The Solid StateSolids are virtually incompressible, owing to the small distance between particles.Melting points depend of the strength of attractive forcesPolar solids have higher melting points than nonpolar of the same molecular weight
24Types of solidsCrystalline: regular repeating structure Amorphous: having no organized
25Types of Crystalline Solids Ionic: positive and negative ions that electrostatic forces hold togetherHigh melting points hard/brittleCovalent: very high melting pointsExtremely hardMolecular: Van der Waals or hydrogen bondingFrequently volatile, soft, low melting points, poor electrical conductorsMetallic: metal atoms, bonds formed by the overlap of orbitals