CHEM 102 FINAL REVIEW - 10.7 The Kinetic-Molecular Theory of Gases Kinetic-Molecular Theory Summary 1 Random motion gases consist of large number

CHEM 102 FINAL REVIEW - 10.7 The Kinetic-Molecular...

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10.7 The Kinetic-Molecular Theory of GasesKinetic-Molecular Theory:Summary1.Random motion:gases consist of large number of molecules that are in continuous random motion2.Negligible molecular volume:the combined volume of all the molecules of the gas is negligible relative to the total volume in which the gas is contained3.Negligible forces:attractive and repulsive forces between gas molecules are negligible4.Constant average KE:energy can be transferred between molecules during collisions, but as long as temperature remains constant, the average kinetic energy of the molecules does not change with time5.Average kinetic energy proportional to temperature:the average KE of the molecules is proportional to the absolute temperature. At any given temperature, the molecules of all gases have the same KE10.8 Molecular Effusion and DiffusionFor two gases as the same temperature a gas composed of low-mass particles has the same average kinetic energy as one composed of more massive particles. The mass of the lower-mass one however allows it to have a higher rms speed.Lighter molar mass -> higher speedThe dependence of molecular speed on mass has two interesting consequences. The first is effusion, which is the escape of gas molecules through a tiny hole. The second is diffusion, which is the spread of one substance throughout a space or throughout a second substance.11.1 A Molecular Comparison of Gases, Liquids, and SolidsLiquidshave intermolecular attractive forces strong enough to hold particles close togetherSolidshave intermolecular attractive forces strong enough to hold particles close together and to lock them virtually in placeGaseshave much weaker interparticle attractions than those that are liquids, and liquidshave weaker attractions than those that are solidsThe state of matter of a substance depends largely on the balance between kinetic energies of the particles and the interparticle energies of attractionKinetic energies, which depend on temp, tend to keep the particles apart and movingInterparticle attractions tend to draw the particles together11.2 Intermolecular ForcesThe strength of intermolecular forces vary over a wide range but are generally much weaker than intramolecular forces - ionic, metallic, or covalent bondsCovalent bonds are strong intramolecular attractionsThree types of intermolecular attractions that exist between electrically neutral moleculesDispersion forces (van der Waals force for nonpolarbonds)Dipole-dipole attractions(van der Waals force for polar bonds)Hydrogen bonding
IMF are strong enough to control properties like melting and boiling pointsAll intermolecular interactions are electrostatic, involving attractions between positive and negative species (like ionic bonds, but a lot weaker due to the “charges responsible for intermolecular forces are generally much smaller than the charges in ionic compounds”)Dispersion Forces

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