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CHAPTER 18 GASES18-1 Kinetic theory of gases changes in temp have a greater effect on the volume of a gas than on the volume of a liquid or solid gas particles are in constant random motion molecules in an ideal gas are considered to be points with no attractive force. THIS IS NOT ACTUALLY TRUE OF REAL GASES an ideal gas is composed of point masses with no volume and no mutual attraction STP-standard temp(0C)and standard press(101.325 kJ/mol or 760mm) 18-2 Boyles Law pressure by a gas depends on number of particles/unit volume average KE of the particles Boyles law-at constant temp(unchanging) V varies inversely P 18-3 applying Boyles Law use the pressure ratio that will provide the desired volume change 18-4 Daltons law of partial pressure total pressure is the sum of the partial pressures of all gases in the container each gas in the mixture exerts its own partial pressure the pressure of a gas collected over water must be corrected for water vapor pressure 18-5 Charles law for each 1C change a gas changes by 1/273 of its volume at OC Charles Law at constant P, V varies directly with KELVIN T 18-6 applying Charles Law 18-7 combined gas law P½1V½1/T½1=P½2V½2/T½2 revisit STP and Kelvin Temp!!! 18-8 Diffusion and Graham's law diffusion is the random scattering of gas particles KE=1/2mvv Graham's Law:the relative rates of diffusion for 2 gases under identical conditions vary inversely as the square roots of their molecular masses light gas molecules(high velocity)diffuse faster than heavier gas molecules at the same temp 18-9 Deviations of Real Gases Joule-Thompson effect:if a highly compressed gas is allowed to escape through a small opening, its temperature decreases the particles of real gases, unlike ideal gases, have both volumeÜjÜŒ and mutual attraction. At high P and low T, these 2 factors take effect At normal lab T and P most common gases behave nearly as ideal gases. the lower Tc of a gas, the more nearly it behaves as an ideal gas CHAPTER 19 GASES AND THE MOLE19-1 Molar Volumethe number of gas molecules in a container determine the pressure at a given temperature Avogadro's principle:under similar conditions, equal volumes of gases contain the same number of molecules(6.02X10¼2¼3) 19-2 Ideal gas equation PV=nRT(status quo) n=#moles R=universal gas constant=8.31 cdmkPa/mol K cdm=cubic decimeters or L the molecular mass of a gas can be determined from lab measurements M=mRT/PV m=mass M=molecular mass D=PM/RT D=density 19-3 Mass-Gas volume relationships Stoichiometry is the quantitative study of chem reactions a balanced equation is necessary for obtaining correct answers to chemical problems 1 mole of a gas occupies 22.4 cmd(L) at STP 19-4 Volume-volume relationships gases are more easily measured by volume than by mass in vol-vol problems the coefficients of the balanced equation are used to determine the ratio of the combining gas volumes the ratio of combining gas volumes is the same as the ratio of combining moles 19-5 Limiting reactants a limiting reactant is completely used in a reaction |
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