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Gas Laws Joseph Louis Gay-LussacAmadeo Avogadro Robert BoyleJacques Charles

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The Combined Gas Law The combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas.

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Boyles Law Pressure is inversely proportional to volume when temperature is held constant.

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Charless Law The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin. (P = constant) Temperature MUST be in KELVINS!

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Gay Lussacs Law The pressure and temperature of a gas are directly related, provided that the volume remains constant. Temperature MUST be in KELVINS!

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Avogadros Law For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas (at low pressures). V = an a = proportionality constant V = volume of the gas n = number of moles of gas

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Ideal Gas Law PV = nRT P = pressure in atm V = volume in liters n = moles R = proportionality constant = L atm/ mol· T = temperature in Kelvins Holds closely at P < 1 atm

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Real Gases corrected pressure corrected volume P ideal V ideal At high pressure (smaller volume) and low temperature (attractive forces become important) you must adjust for non-ideal gas behavior using van der Waals equation.

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Gas Density … so at STP…

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Density and the Ideal Gas Law Combining the formula for density with the Ideal Gas law, substituting and rearranging algebraically: M = Molar Mass P = Pressure R = Gas Constant T = Temperature in Kelvins

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Gas Stoichiometry #1 If reactants and products are at the same conditions of temperature and pressure, then mole ratios of gases are also volume ratios. 3 H 2 (g) + N 2 (g) 2NH 3 (g) 3 moles H mole N 2 2 moles NH 3 3 liters H liter N 2 2 liters NH 3

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Gas Stoichiometry #2 How many liters of ammonia can be produced when 12 liters of hydrogen react with an excess of nitrogen? 3 H 2 (g) + N 2 (g) 2NH 3 (g) 12 L H 2 L H 2 = L NH 3 L NH

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Gas Stoichiometry #3 How many liters of oxygen gas, at STP, can be collected from the complete decomposition of 50.0 grams of potassium chlorate? 2 KClO 3 (s) 2 KCl(s) + 3 O 2 (g) 50.0 g KClO 3 1 mol KClO g KClO 3 3 mol O 2 2 mol KClO L O 2 1 mol O 2 = 13.7 L O 2

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Gas Stoichiometry #4 How many liters of oxygen gas, at 37.0 C and atmospheres, can be collected from the complete decomposition of 50.0 grams of potassium chlorate? 2 KClO 3 (s) 2 KCl(s) + 3 O 2 (g) 50.0 g KClO 3 1 mol KClO g KClO 3 3 mol O 2 2 mol KClO 3 = mol O 2 = 16.7 L 0.612

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Daltons Law of Partial Pressures For a mixture of gases in a container, P Total = P 1 + P 2 + P This is particularly useful in calculating the pressure of gases collected over water.

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