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Properties of Gases

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Properties of Gases

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    1. Properties of Gases Gases and liquids are fluids No fixed volume Fill whatever container they are in Diffuse easily Low density Compressible

    3. The Atmosphere Sea (mixture) of gases Know major components Functions Traps energy near earth's surface Greenhouse effect Keeps the planet warm Know greenhouse gases Filter radiation coming to earth Ozone depletion CFC's, freon Know uses of CFCs

    5. Kinetic Theory of Gases Ideal gases Vol of each gas particles are essentially 0 Gas particles are in constant straight line motion until they hit something No forces (attraction or repulsion) act between gas particles The average Ek (movement) a gas particles is directly related to their Kelvin temp Remember Boltzman's curve

    6. Boltzmanns Curve of Molecular Velocities

    7. A Description of Gases 4 variable are needed to fully describe a gas sample Temp K temp is directly related to many properties K = C + 273 Vol Space the gas occupies L or mL Amount of gas Moles A specific number of particles Mol = grams gas molar mass of the gas Molar volume of gas = 22.4 L Pressure

    8. Pressure Pressure = force area Gas particles create pressure by colliding with the sides of their container Temp and press are directly related Increase temp and press increases Vol and press are inversely related Increase vol and press decreases

    9. Measuring Gas Pressure

    10. Units of Pressure Pascal = 1.0 newton/meter2 KPa = 1000 Pa 101.3 KPa = 760 mm Hg = 1.0 Atmospheres atm x 760 mm Hg/atm = mmHg atm x 101.3 KPa/atm = Kpa mmHg 760 mm Hg/atm = atm Kpa 101.3 Kpa/atm = atm

    11. How many mm Hg in 1.50 atm? How many atm are present in a gas at 1234 mm Hg?

    12. How many mm Hg are in a system at 0.159 atm? What is the pressure in atm of a gas at 459 mm Hg?

    13. Measuring Gas Pressure Manometer Used to measures gas pressure in a closed system

    14. Changes in P, V, n, and T Relate all changes to the KMT! What happens to the V of a gas sample if you add more gas to the sample (increase # moles)? What happens to the P or of a gas sample if you increase it's temp? What happens to the P of a gas sample if you add more gas to the sample (increase # moles)? What happens to the or V of a gas sample if you increase it's temp? What happens to the V of a gas sample if you increase it's pressure? What happens to the P of a gas sample if you increase it's volume?

    15. Gas Laws Mathematical descriptions of how gases behave Gases that follow the gas laws are said to act in an ideal manner Equations relate 4 variables P = pressure V = volume n = moles T = temp (K only)

    16. Gas Laws Avogadro's Law Boyles Law Molar vol of a gas Press vs vol Charles Law Guy-Lussacs Law Temp vs vol Press vs temp Grahams Law How gas particles diffuse Daltons Law Press in a mixt of gases

    17. Avogadro's Law n1 n2 v1 v2 Under the same conditions of temp and press, equal number of gas particles occupy the same volume. One mole of any gas occupies the volume

    18. Molar Volume of Gas Standard Temp and Press 0C or 273 K and 760 mm Hg, 1 atm, or 101.3 KPa At STP 1 mol of any gas occupies 22.4 L 1N2(g) + 3H2 (g) ? 2NH3 (g) Coefficients represent molec:molec mol:mol Vol:vol

    19. Charles Law V1 V2 Directly relation T1 T2 V1 and V2 must be in the same units L or mL T1 and T2 must be in Kelvins Used to calc a new vol when the temp of a gas sample has changed

    20. Boyles Law P1V1 = P2V2 Inversely Related P1 and P2 must be in same units Mm Hg, atm, or KPa V1 and V2 must be in same units L or mL Used to calc new P or V with changes in the other

    22. Guy-Lussacs Law T1 T2 Directly relation P1 P2 Refrigeration compressors and air conditioners Temps must be in K P1 and P2 must be in same units

    23. Graphs of Math relationships Direct Inverse

    24. Combined Gas law P1V1 = P2V2 T1 T2 Used to calc a new condition when 2 other conditions change

    25. Sample Problem A sample of CO2 occupies 125 mL at 25C and 750 mm Hg. What vol will it occupy at STP? P1 = 750 mm Hg T1 = 25 + 273 K v1 = 125.0 mL P2 = 760 mm Hg T2 = 273 v2 = x mL P1V1 = P2V2 or V2 = P1V1T2 T1 T2 T1P2 V2 = P1V1T2 = 750 mm Hg x 125 mL x 273 K = 113 mL T1P2 298 K x 760 mm Hg

    26. Ideal Gas Law PV = nRT R = 0.0821 L atm/molK All units must be the same as in R (L, atm, mol, and K) P = pressure in atm mm Hg 760 mm Hg/atm V = vol in L mL 1000 n = moles g molar mass T = kelvins C + 273

    27. Conversions Units of R P: mm Hg 760 mm Hg/1 atm = atm Convert 750 mm Hg to atm n: g mm = moles Convert 27.3 g CH4(mm = 16.0 g/mol) to mol K: C + 273 = K Convert -17.5 C to Kelvins

    28. Sample Problem A 125 mL sample of hydrogen gas at 20C exerts a pressure of 800 mm Hg. a. Calc the number of mol of gas in the sample. PV = nRT P = 800 760 atm = 1.05atm V = 125 1000 L = 0.125 L T = 20 + 273 = 293 K n = PV = (1.05 atm)(0.125 L) = 0.00546 mol H2 RT (0.0821 L atm/mol K) (293 K) b. Calc the number of grams of gas in the sample. 0.00546 mol H2 x 2.0 g = 0.0109 g H2 1 mol H2

    29. Amounts gases at STP

    31. How many grams of water are produced by the reaction of 2.0 L of hydrogen gas @ 25C and 1.0 atm pressure? 2H2 + O2 ? 2H2O Plan: n = PV/RT mol ratio mol x g g H2 mol H2 mol H2O grams H2O 1 2 3 1. n = (1.0)(2.0) = 0.082 mol H2 0.0821 (25 + 273) 2. 0.082 mol H2 x 2 mol H2O = 0.082 mol H2O 2 mol H2 3. 0.082 mol H2O x 18.0 g/mol = 1.5 g H2O

    32. How many liters of water are produced by the reaction of 4.0 g of hydrogen gas @ 25C and 1.5 atm pressure? 2H2 + O2 ? 2H2O Plan: g/mm = mol H2 mol ratio V = nRT/P g H2 mol H2 mol H2O L H2O 1 2 3 1. 4.0 g /2.0 g/mol = 2.0 mol H2 2. 2.0 mol H2 x 2 mol H2O = 2.0 mol H2O 2 mol H2 3. V = (2.0 mol)(.0821Latm/molK)(273 + 25K)/1.5 atm = = 32.6 L

    35. Gas Stoichiometry Air bags in cars are inflated by N2 gas generated by the rapid decomposition of sodium azide, NaN3: 2NaN3 ? 2Na (s) + 3N2 (g) If an airbag has a volume of 36 L. If it is to be filled with 1.15 atm of N2 at 26.0C, how many grams of NaN3 must be decomposed to fill it? vol N2 mol N2 mol NaN3 grams NaN3

    36. Liquid Vapor Equilibrium Evaporation = vaporization of a liquid at temps below the boiling point The pressure created by the vaporization of a liquid in a closed container at constant temperature Determined by strength of IMF Inversely related

    37. Vapor Pressure Pressure of a gas above a liquid A type of equilibrium 2 opposing processes occurring at the same rate Caused by the evaporation of the liquid Related to IMF Increases with increasing temp Table A-4 p 795

    38. Dynamic Equilibrium Liq Vapo Introduce liq into a sealed system Evaporation begins Liq Vapor Evaporation continues and condesation begins begins Liq Vapor Eventually the rates of the 2 opposing processes equal each other

    39. Vapor Pressure The vapor above a liquid produces a constant pressure at a constant temperature Table on pg 794 vp and temp are directly related Vp and IMF are inversely related

    40. Daltons Law The total pressure in a gas mixture is the sum of the partial pressures of the individual gases if alone in the same container

    41. Mole Fraction In a gas mixture (more than one type of gas) the partial pressure of each gas is determined by the number of molecules of each gas present

    42. Mole fraction MF = # mol Gas A Total # mol of gases in the sample Oxygen makes up 20% of the air. What is oxygen's mole fraction? If 20% of air is O2, then, 100 moles of air contain 20 moles of O2.

    44. Dalton's Law of Partial Pressure 2-The pressure of the components of a gas mixture is relative to their percents or mole fraction Mol frac = mole gas A total moles gases I know it's a decimal, but it's called mole fraction!!! Mol fraction is the same as percent PgasA = Ptotal x MFgasA or PgasA = Ptotal x PercentgasA(as a decimal)

    45. Dalton's Law of Partial Pressure A gas sample contains 2.0 mol O2, 1.0 mol N2, and 3.0 mol He. Determine The mol fraction of each gas. MFO2 = 2.0/6.0 = 0.33 MFN2 = 1.0/6.0 = 0.17 MFHe = 3.0/6.0 = 0.50 The partial press of each gas if the total press on the system = 950 mm Hg PPO2 = 950 x 0.33 = 314 mm Hg PPO2 = 950 x 0.17 = 162 mm Hg PPO2 = 950 x 0.50 = 475 mm Hg

    47. Gases Collected over H2O A 152 mL sample of H2 gas is collected under water at 25C (vpH2O= 23.76 mm). If the sample exerts a pressure of 758 mm Hg determine: a. the partial pressure of the H2 Ptotal = PH2O + PH2 Ptotal - PH2O = PH2 758 - 23.76 = 734 mm Hg b. the grams of H2 collected nH2 = PH2V = (734 / 760 atm)(0.152 L) = 0.00600 mol O2 RT (0.0821 L atm/mol K)(298K) = 0.00600 mol H2 x 2.0 g = 0.012 g H2 mol

    48. Graham's Law of Effusion Under the same conditions, heavier gases travel slower. How much slower a gas travels is related to the molar mass of the gases vela mmb velb mma A gas 2x heavier will travel as fast A gas 4x heavier will travel as fast

    49. Ideal vs Real Gases Ideal gases behave according to the gas laws Most gases at room conditions are ideal Under very low temp or very high press gases don't obey the gas laws 2 assumptions of the KMT are incorrect No forces act between molecules The volume occupied by gas molecules is negligible

    51. Boiling Point Temp at which the vapor pressure above the liquid equals the atmospheric pressure Stronger IMF = higher bp What happens to bp at high altitudes? Why?

    52. Phase Diagram

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