The state of a substance at a particular temperature and pressure depends on two things Kinetic Molecular Theory 1 The kinetic energy of the particles 2 The strength of the attractions between the particles KE IM Gas KE IM Liquid KE IM Solid Kinetic Energy is proportional to temperature KE T Intermolecular Forces non covalent interactions Weaker than covalent bonds IntRA molecular bonds are much stronger than IntER molecular forces Strength of IM forces depend on o Polarizability ease with which electron clouds become distorted increases as number of electrons increases increases as size MW increases o Q The charge on the ion o The dipole moment Types of Intermolecular forces dependent on o Ion Ion Q Opposite charges attract covalent bonds E Q1Q2 r o Ion Dipole Q Ions in aqueous solutions of electrolytes E Q r2 Example Salt dissolved in water o Dipole Dipole E Q1Q2 r3 Example hydrochloric acid o Ion Induced Dipole Q Ions in nonpolar solvents An ion by a neutral molecule o Dipole Induced Dipole Polar molecules in nonpolar solvents E 1 2 r6 o Dispersion o Hydrogen Bonding directional Dipole Dipole Must have H bonded to N O F When Hydrogen is bonded to NOF the hydrogen nucleus is exposed Weak compared to covalent bonds but are directional like them Strong as intermolecular forces go 4 25kJ mole IM force but DIRECTIONAL like covalent bonds IM forces are due to ELECTROSTATIC attraction Boiling points increase as dispersion forces increase mainly MW Assume the shape of the container have low densities are compressible Ideal Gases Gases form homogeneous mixtures in all proportions The five postulates 1 Molecules move in straight lines direction is random 2 Molecules are small the volume they occupy is small compared to total V 3 Molecules do not attract or repel each other no intermolecular forces 4 Elastic collisions 5 MEAN kinetic energy T K Temperature is proportional to average kinetic energy T so related to speeds 5mu2 average kinetic energy of molecule U root mean square speed of molecule m mass of molecule in kg Molecules move at different speeds When T increases the average speed increase Lighter gas moves faster than heavier gas Rms speed u 3RT M 5 Manometer is used to measure difference in pressure in a gas vessel Pgas Patm Ph When the end is closed Patm 0 Diffusion is the spread of gas through space Effusion is the leakage of gas through a small opening Rate of effusion 1 M 5 Graham s Law r1 r2 M2 M1 5 Heavy molecules effuse diffuse more slowly than lighter molecules Avogadro s Law V of a gas at constant T and P is proportional to the number of moles Boyles Law V of a fixed amount of gas is inversely proportional to P Charles s Law V of fixed amount of gas at constant P is proportional to the absolute Temp Combine them to get the Ideal Gas Equation PV nRT STP 0 C and 1 atm VSTP L mol D nM V PM Rt M dRT P Non Ideal Gases As P increase non ideality increases As T decreases non ideality increases Partial Pressure the pressure a gas would have if it was the only gas in the container Dalton s Law of Partial Pressure Total pressure is equal to the sum of partial P s The fraction of the total pressure contributed by each gas is equal to its mole fraction Xi Pi PTOT ni nTOT Thermochemistry is the study of energy changes in chemical processes 2H2 O2 2H2O energy Kinetic and Potential Energy First Law of Thermodynamics E q w Enthalpy is heat transferred at constant P E qp wp qp P V P is constant So qp E P V defines H Enthalpy H is heat transferred at constant P H H products H reactants 1 Enthalpy is an extensive property 2 H for a reaction is equal in magnitude and opposite in sign to H for the reverse reaction 3 H for a reaction depends on the states of reactants and products gas liquid solid CALORIMETRY is the experimental measure of heat flow o q Cm T q heat flow C specific heat heat capacity per gram m mass o Hess Law H for a sum of steps is the same as H for the overall process Standard states of elements o The most standard form of an element at 298 K and 1 atm STP o Metals all solids except mercury o Metalloids all solids o Atomic gases He Ne Ar Kr Xe Rn o Diatomics halogens and H2 N2 O2 gas Halogens group 7 F2 gas Cl2 gas Br2 liquid I2 solid o Other nonmetals solids C graphite S P Se Bond order number of covalent bonds BOND STRENGTH is the energy needed to break a covalent bond o Shorter bond Stronger bond o More shared pairs higher the bond order stronger and shorter bond Bond Energy D is the enthalpy needed to break a bond for a molecule in the gas phase o Bond energies provide estimates of reaction enthalpies Hrxn Hrxn nDbroken nDformed n m number of bonds energy is given off when bonds form Viscosity is the measure of the resistance to flow o Cohesive forces viscosity o For a pure compound as T viscosity Surface Tension is the energy needed to increase surface area o cohesive forces surface tension Capillary Action is the result of adhesion and surface tension Hfusion amount of heat needed to melt a mole of substance Hvap amount of heat needed to vaporize a mole of substance 1 Within single phase slanted lines changes are continuous 2 Between phases horizontal lines the changes are from one physical state to another a Q nCm T a Q n Hx Vapor Pressure vp is the pressure exerted by a vapor in equilibrium with its liquid or solid phase o In dynamic equilibrium o Forward Rate Backward Rate and Evaporation Condensation o No net change but change is occurring on a molecular lever o Boiling point temperature at which v p Pext Solutions Homogenous Mixture is uniformly mixed on a molecular level o Solute the component of a mixture that is present in smaller quantity o Solvent the component of a mixture that is present in greatest quantity o Aqueous Solutions water is the solvent Electrolytes o Strong Electrolytes good conductors NaCl S H2O Na aq Cl aq H2O HCl aq H2O H3O aq Cl aq o Weak Electrolytes poor conductors NH3 aq H2O NH4 CH3COOH aq H2O CH3COO aq H3O aq o Nonelectrolytes non conductors do not conduct electricity Glucose C6H12O6 s H2O C6H12O6 aq H2O Alcohols Carbohydrates Aldehydes Ketones aq OH aq o An acid base or salt Strong acids and bases are strong electrolytes Ionic compounds are strong electrolytes Weak acids and bases are weak electrolytes Molecular compounds neither acid or base are nonelectrolytes Expressing Concentration o Mass fraction mass of component total mass Ppm mass fraction x 106 Ppb mass fraction x 109 Ppt mass fraction x 1012 o Weight mass fraction x 100
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