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Unformatted text preview: Pressure Lecture 21 Topics Barometer: P = dhg Units: Pa, atm, Torr, mmHg, etc. Gas Laws Boyle's Law: V vs. P Charles' Law: V vs. T Avogadro's Principle Ideal gas law: PV = nRT Gas Density: d = MP/RT Pressure
P = dhg d = density of liquid h = height of column g = acceleration of gravity Units of pressure: Pascal, atm, Torr, mmHg, bar Boyle's Law
V = constant/P at constant n and T Charles' Law
V = constant x T at constant n and P Avogadro's Principle
one mole of any gas occupies same V At 0C and 1 atm Ideal Gas Law
PV = nRT
True at ideal conditions: Low P and not low T This is when the molecules interact the least and therefore are more "ideal" Combined gas law: P1V1/n1T1 = P2V2/n2T2 Gas Density
Density = mass/volume In a gas, density = MP/RT Larger molar mass, M = high density Small molar mass, M = low density High temperature = low density Low temperature = high density Lecture 23 Topics Gas Stoichiometry same info, different phase moles to volume using molar volume Gas Mixtures law of partial pressures mole fractions Gas Stoichiometry
2NaN3(s) 2Na(s) + 3N2(g) Gives same information as other phases reactants needed products produced Molar volume converts moles to volume and vice versa Partial Pressures
Law of Partial Pressures P = PA + PB + ... P = (0.4 + 0.6) atm = 1.0 atm Mole Fractions xA = PA/P = nA/n Lecture 24 Topics Molecular Motion diffusion vs. effusion speed vs. temperature, molar mass Maxwell Distribution of Speed f(v) = 4 (M/2RT)3/2 v2e-Mv /2RT
2 Kinetic Model of Gases vrms = (3RT/M)1/2 molar KE = 3RT/2 Diffusion - movement of one substance through another Molecular Motion Effusion - gas escaping through a hole from high P to low P Rate of effusion (T/M)1/2 Speed (T/M)1/2 Maxwell Distribution of Speed
Not all molecules have the same speed, there is a distribution dependent on M and T f(v) = 4 (M/2RT)3/2 v2e-Mv /2RT Kinetic Model of Gases
Gas molecules are constantly traveling in straight lines until they collide with walls or other molecules. vrms = (3RT/M)1/2 Molar KE = 3RT/2 Lecture 25 Topics Real Gases van der Waals equation deviation from ideality Intermolecular Forces ion-ion ion-dipole dipole-dipole London dispersion Real Gases: van der Waals equation
" n2 % $ P + a 2 '(V ( nb) = nRT V & # a = accounts for intermolecular forces b = represents volume of molecule ! Intermolecular Forces Attractions between molecules/atoms Effect of Intermolecular Forces more intermolecular forces, more attraction, higher boiling point Lecture 26 Topics Properties of Liquids Viscosity Surface Tension Capillary Action Types of Solids Molecular Network Properties of Liquids
Viscosity - resistance to flow Depends on: - intermolecular forces - temperature - chain length, longer and bulkier chains tangle Properties of Liquids
Surface tension - higher for molecules with more intermolecular forces Capillary action - adhesion vs. cohesion. Mercury has more cohesion, water has more adhesion Types of Solids
1. Molecular Solids - molecules held together by intermolecular forces - ex. Paraffin wax, "bullet proof" vest - properties depend on forces 2. Network Solids- atoms covalently bound to neighboring atoms - ex. diamond, each C is bound to C - Ceramic materials SiO2, quartz, glass Lecture 27 Topics Types of Solids (continued) Metallic Structure of Solids face-centered cubic body-centered cubic unit cells Ionic Structures Types of Solids
3. Metallic solids - cations held together by a "sea" of electrons
hexagonal close-packed cubic close-packed 74% space occupied, 26% empty Unit Cells smallest unit that when stacked together represents entire crystal Cubic Unit Cells Ionic Structures
Zinc-blende Rock salt Cesium chloride < 0.4 = 0.4-0.7 > 0.7 Which structure depends on radius ratio, THE END!!
Final Exam on Friday, 12/11, 3-6PM in 2722 York Hall ...
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This note was uploaded on 04/29/2010 for the course CHEM CHEM 6A taught by Professor Czarkowski during the Spring '07 term at UCSD.
- Spring '07