Name Constant Proportionality Standard form Boyles n, T V α 1/P P 1 V 1 = P 2 V 2 Charles n, P V α T =

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1 Ch 0 GASES Gases represent matter in its most diffuse, disorganized energetic state GENERAL PROPERIES OF GASES: Gases may be compressed Gases expand to fill their containers 3 Gases have low densities 4 Gas molecules move very fast & have high KE PRESSURE - measure of force per unit area Pressure is the result of the gas molecules colliding with surface Barometer - device used to measure atmospheric pressure Important Pressure Units & conversion factors: KNOW: mm Hg torr; atm 760 mm Hg 760 torr (exact numbers SI unit is Pascal: atm 035 x 0 5 Pa (don't need to memorize Pascal GAS LAWS Many scientists examined relationships between variables associated w/ gases 4 variables: P pressure, volume, temperature, n number of moles Name Constant Proportionality Standard form Boyles n, α /P P P Charles n, P α Avogadro P, α n Combined Gas Law n P α P n NOE: For gas problems, need to use temperature in Kelvin If given C convert to K: K C + 73 SP conditions: Standard temp: 73 K 0 C; Standard Pressure: P atm 760 torr Molar volume is the volume occupied by mole of a gas at a given & P 4 L At SP, mole of any gas occupies 4 L Molar volume mole P nr IDEAL GAS EQUAION: L atm Ltorr R gas constant R 008 or 64 K mol K mol We can also use ideal gas law to solve for mass (g, molar mass or density MM P d R n P

2 GAS SOICHIOMERY g or L Given moles given moles wanted g or L Wanted Can use ideal gas equation to convert from volume (L moles; at SP can use 4 L/mol GAS MIXURES Dalton's law of partial pressure: he total pressure of a mix of gases is the sum of the partial pressures of the individual gases P otal P A + P B + P n R C where P A A, etc KINEIC MOLECULAR HEORY - explains behavior & properties of gases Gases consist of tiny particles that are in constant, rapid motion Gas molecules are far apart from each other & the volume occupied by a gas is mostly empty space 3 Attractive forces between gas molecules are negligible 4 When molecules collide, energy can be transferred, but there is no net energy loss (ie collisions are elastic 5 At a given temperature, the particles of all gases have the same average KE he average KE of a gas is proportional to the temperature KE Distribution for gases Not all molecules in a sample of gas move at the same speed his is represented by the following kinetic energy distribution: molecular speed u speed of molecule with average kinetic energy at the higher temp, more molecules move faster and the average speed is higher at a given temperature, the average KE is the same for gases, but gas molecules with lower MM will move faster: KE /mv mass & velocity are inversely proportional DIFFUSION S EFFUSION Diffusion - spreading out of gas molecules to occupy the total volume in which they are confined eg perfume in room Effusion - passage of gas molecules through a barrier with tiny hole(s in it GRAHM'S LAW: rate A rate B MM B MM A Lighter gases (lower MM effuse & diffuse more rapidly than heavier gases Eg He effuses out of a balloon more rapidly than N so He balloons shrink faster H diffuses faster through room than N Place the following molecules in order of increasing rate of effusion: CO, H S, Cl, HF

3 Real Gases Deviate from ideal behavior Reasons: Assumption that gas molecules occupy no space is false, gas molecules do have finite volumes At low pressures, the volume that gas molecules occupy is very small and can be ignored; but at high pressures, gas molecules occupy a sizable % of total volume Gas molecules do have attractions for one another(km #3 is not valid At high temps, molecules move faster and intermolecular forces can t form; but at low temps, gas molecules move slower and have intermolecular attractions - approach liquid state Also, at high pressures, gas molecules are closer together so attractive forces can develop between molecules Gases behave ideally (obey KM at low pressure and high temperature Gases deviate from ideal behavior at high pressure and low temperature

4 Gas Law Problems I A variable volume container holds 43 L of a gas at 55 C What will the temperature be if the volume is decreased to 55 L? 43 L 55 C K 55 L? so ( smaller term on top ( 55 L ( 38 K ( 43 L 09 K he pressure on 648 ml of a gas is changed from 77 torr to 695 torr What is the volume at the new pressure? 648 ml P 77 torr P 695 torr? P P P P P so (bigger P term on top ( 77torr ( 648ml ( 695torr 70 ml 3 A gas occupies 33 L at SP What pressure (in torr will this gas exert if it is expanded to 69 L and warmed to 7 C? P 760 torr 33 L 73 K P? 69 L K P P 33L 90 K P P 760 torr 69 L 73K 304 torr 4 he gas in a 077 L cylinder exerts a pressure of 744 torr at 7 C What volume will it occupy at 486 atm and 547 C? atm 077 L P 744 torr 0979 atm K 760torr? L P 486 atm K P P 077 L 0979atm 80 K 486atm 300 K L 5 How many grams of CO are present in 50 L of CO at SP? SP: 4 L/mol mol 440 g 50 L 4 L mol 49 g CO

5 6 Calculate the density of SF 4 at 650 torr and 00 C atm P 650 torr 0855 atm K 760torr g 08 ( 0855atm MM P d mol 30 g/l R Latm 008 ( 373K Kmol GAS PROBLEMS II What is the Molar Mass of a gas if 086 g occupy 500 ml at 55 K and 75 torr? dr MM dr P MM P 086 g atm d 57 g/l P 75 torr 0954 atm 0050 L 760torr 57 g 008 L atm 55 K L MM K mol 6 g/mol 0954atm Calculate the grams of H O that would result from combustion of 9 L of CH 4 at 083 atm and 6 C CH 4 (g + O (g CO (g + H O(l L CH 4 mol CH 4 mol H O g H O P nr P 083 atm, 9 L, K 99 K P ( 083atm( 9 L n 0636 moles CH 4 R 008L atm ( 99K K mol mol H O 8 0 g H O 0636 moles CH 4 9 g O mol CH 4 mol H O 3 What volume of O gas can be collected at SP during the decomposition of 0357 g KClO 3 to form KCl and O KClO 3 KCl + 3O g KClO 3 mol KClO 3 mol O L O mol KClO 3 3mol O 0357 g KClO 3 6 g KClO 3 mol KClO moles O L O at SP: 4 L/mol 3 437x0 437x0-3 4 LO moles O L O mol O 3 moles O

6 4 How many liters of hydrogen gas at 5 atm and 8 C can be produced by the reaction of 550 ml of 66 M HCl with 45 g of Al? Write the balanced reaction first! 6HCl + Al AlCl 3 + 3H LR problem: find moles of hydrogen produced from each reactant L HCl mol HCl mol H g Al mol Al mol H L 66 molhcl 3mol H 550 ml HCl 000 ml L 6mol HCl mol Al 45 g Al 3mol H 70 gal 05 mol H mol Al 08 moles H is smaller amount, HCl is LR 08 mol H Find L H : P 5 atm, n 08 moles, K 008Latm ( 08mol H ( 9K nr Kmol P nr 344 L H P 5atm (