Review of CHM 1316 Final at 11 AM Monday 7 May 2001 Gases and Chemistry of the Atmosphere Ideal Gas Laws Relation of Temperature to KE Earth s Atmosphere Ideal Gas Law PV nRT Boyle s Law for isotherms P1V1 P2V2 Charles Law for isobars V1 T1 V2 T2 Avogadro s Law for moles V1 n1 V2 n2 For adiabatic processes q 0 T1 P1 T2 P2 where CP CV 1 4 So T falls as P falls with altitude in atmosphere Pressure Work Energy P 1 Pa Pascal 1 N m 2 force area Gravitational force weight of Earth s atmosphere above every m2 is 101 325 Pa 1 atm 101 325 kPa 760 mm Hg torr 1 bar 100 kPa 0 986923 atm R 0 08206 atm L mol 1 K 1 R 8 314 J mol 1 K 1 PV Nm J energy work P V Standard Conditions For Gases P 1 bar For Thermodynamics P 1 bar T 0 C 273 15 K Unit amount n 1 T 25 C 298 15 K Unit amount n 1 mole 6 022 1023 molecules mole 6 022 1023 molecules Non ideal Gases Many equations of state for real gases Van der Waals a good approximation Preal a n Vreal 2 Vreal n b n RT Pideal exceeds Preal by gas gas attraction a Vreal exceeds Videal by molecular volume b Equipartition Theorem kinetic energy mmoleculevrms2 kT k Boltzmann constant R NAv KINETIC ENERGY Mvrms2 RT 3 Cartesian Directions KE 3 2 RT Effusion from puncture and Diffusion through gas v12 v22 M2 M1 Graham distance v t so heavy takes longer than light CV monatomic gas 3 2 R Earth s Atmosphere Dry Air 78 N2 21 O2 1 Ar and traces esp 365 ppm CO2 Sat d Air 95 of above 5 water vapor Troposphere weather by buoyancy Rising hot air cools adiabatically condenses H2O Stratosphere stagnant by O 3 hv O O2 Traces NOX SOX give Acid Rain Growing CO2 traps IR warms Earth Pure Solids and Liquids Intermolecular forces Crystals and Metals Phase Diagrams Intermolecular Forces London induced dipole induced dipole Enhanced by size and weakly held electrons Dipole Much higher melting points X H X hydrogen bonding with X N O F Ionic Strongest forces but ion dipole often competes as in dissolution in aqueous solution Phase Properties Solids Immobile and often regular arrays Liquids Molecules migrate but remain cohesive Surface tensions yield capillarity Gases Free molecular motion fills container Found vapors in increasing concentration as solids liquefy until PVAPOR 1 atm defines boiling Solid Organization Amorphous absence of order e g glass Crystalline repeating unit cell patterns Molecular London or Dipolar binding Atomic macroscopic molecules Covalent diamond or Metal binding Ionic also macroscopic Cation Anion binding Easily shattered along glide planes Regularity 7 Crystal Systems A consequence of packing unit cells in 3d Coherent X ray scattering Bragg angles n 2d sin give constructive interference patterns d measures plane separations Miller indices Absences in the indices forced by symmetries Geometries and dimensions of molecules in unit cells prove molecular structure Phase Diagrams fixed P T Coexistence lines of melting boiling and sublimation Critical Point above which no liquid Triple Point where 3 phases coexist Critical point Pc 218 Pressure atm Phases co existing at 10 252 Solid Liquid 1 00 P3 0 0060 Gas Triple point Tm T3 Tb Tc 0 0 0098 100 374 Temperature C Metal Bonding Infinite in extent throughout metal crystal Overlap of NAv valence orbitals gives bands of whole crystal molecular orbitals Metal properties if filled MO since kT sufficient to excite electrons Fully filled MO but overlaps empty bands Semiconductor properties if Electronic gap to next vacant band can only be bridged with applied voltage Egap Solvents and Solutes Ideal solutions Colligative properties Non idealities Impetus to Dissolve Endothermic breaking of pure bonding offset by solvent solute interactions Adhesive forces compete with cohesive Like dissolves like ensures comparable force magnitudes Water the universal solvent Polarity surrounds and insulates ions Hydrogen bonds dissolve oxygen containing solutes Entropy wins Ideal Solutions Raoult s Law Psolvent Xsolvent P solvent Henry s Law Psolute Xsolute KHenry Valid if cohesion adhesion Valuable to measure chemical activity of solution components by vapor pressures Violated as a rule deviation if cohesive adhesive forces deviation if cohesive adhesive forces Colligative Properties Depend only on mole fraction not identities Freezing Point Depression Tfp solvent kfp solvent msolute Boiling Point Elevation Tbp solvent kbp solvent msolute Osmotic Pressure solvent Csolute RT van t Hoff factor i neff ndissolved Measures of Solutes Mole fraction Xi ni nj Measures apples and apples Molarity Mi ni 1 Lsolution Valuable for dispensing Suffers if solution densities vary with conc Molality mi ni 1 kgsolvent While V may not be conserved mass always is Aqueous m M at infinite dilution Thermochemistry Conservation of state functions Enthalpy the Chemist s choice Exo and Endothermicity Energy E q w q heat transfer of energy by T w work transfer of energy by organized force EUniverse 0 is Thermodynamics 1st Law Heat Capacity CV dE dT V E T E qV or heat transferred at fixed volume Exothermic process sheds heat E 0 Endothermic process absorbs heat E 0 Work Work travel through force F x Surface tension Work A that increases energy with surface area Pressure Volume Work increases energy with decreasing volume against expansive force so w P V Electrical work Q E where E is an electrical potential difference through which charge Q travels Enthalpy H H E PV H E P V assuming P fixed H qP or heat transferred at fixed P CP dH dT P H T is the heat capacity at fixed P Exothermicity means H 0 fixed P Endothermicity means H 0 State Functions INDEPENDENT of any process s path Examples E H T P V S A and n NON State Functions include w and q The basis of Hess s Law State Function the same over all paths Pick the easiest to measure or compute H vi Hf vi are product stoichiometric coefficients but negative reactant stoichiometric coefficients Standard States Elements The state most stable at 1 bar and 25 C Enthalpy of formation from elements 0 00 Gases 1 bar at 25 C Pure condensed phases 1 bar at 25 C Ideal Solutes 1 M at 1 bar and 25 C Thermodynamics Entropy and Disorder of the Universe Free Energy G points to Equilibrium Temperature Dependence of K Entropy and Disorder S k ln W Boltzmann s epitaph Equivalent Ways of finding a molecule S increases with heat qrev but cold systems are more influenced than hot already chaotic ones S qrev T Disorder means more Ways of finding the Universe and Disorder Entropy never decreases 2nd Law Ssolid Sliquid Sgas and Ssimple