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Ch. 12 & 13 - Gases III. Two More Laws Ideal Gas Law & Daltons Law

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V n A. Avogadros Principle b Equal volumes of gases contain equal numbers of moles at constant temp & pressure true for any gas

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PV T VnVn PV nT B. Ideal Gas Law = k UNIVERSAL GAS CONSTANT R= L atm/mol K R=8.315 dm 3 kPa/mol K = R You dont need to memorize these values! Merge the Combined Gas Law with Avogadros Principle:

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B. Ideal Gas Law UNIVERSAL GAS CONSTANT R= L atm/mol K R=8.315 dm 3 kPa/mol K PV=nRT You dont need to memorize these values!

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GIVEN: P = ? atm n = mol T = 16°C = 289 K V = 3.25 L R = L atm/mol K WORK: PV = nRT P(3.25)=(0.412)(0.0821)(289) L mol L atm/mol K K P = 3.01 atm C. Ideal Gas Law Problems b Calculate the pressure in atmospheres of mol of He at 16°C & occupying 3.25 L.

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GIVEN: V = ? n = 85 g T = 25°C = 298 K P = kPa R = dm 3 kPa/mol K C. Ideal Gas Law Problems b Find the volume of 85 g of O 2 at 25°C and kPa. = 2.7 mol WORK: 85 g 1 mol = 2.7 mol g PV = nRT (104.5)V=(2.7) (8.315) (298) kPa mol dm 3 kPa/mol K K V = 64 dm 3

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D. Daltons Law b The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases. P total = P 1 + P

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GIVEN: P O2 = ? P total = 1 atm P CO2 = torr P N2 = torr WORK: P total = P CO2 + P N2 + P O2 1 atm = atm atm + P O2 P O2 = atm D. Daltons Law b Three of the primary components of air are CO 2, N 2, and O 2. In a sample containing only these three gases at a pressure of 1.00 atm, P CO2 = torr and P N2 = torr. What is the partial pressure of O 2 ? = atm = atm

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D. Daltons Law When H 2 gas is collected by water displacement, the gas in the collection bottle is actually a mixture of H 2 and water vapor. Water exerts a pressure known as water-vapor pressure So, to determine total pressure of gas and water vapor inside a container, make total pressure inside bottle = atmosphere and use this formula: P atm = P gas + P H 2 O

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GIVEN: P H2 = ? P total = 94.4 kPa P H2O = 2.72 kPa WORK: P total = P H2 + P H2O 94.4 kPa = P H kPa P H2 = 91.7 kPa D. Daltons Law b Hydrogen gas is collected over water at 22.5°C. Find the pressure of the dry gas if the atmospheric pressure is 94.4 kPa. Look up water-vapor pressure on p.899 for 22.5°C. Sig Figs: Round to least number of decimal places. The total pressure in the collection bottle is equal to atmospheric pressure and is a mixture of H 2 and water vapor.

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GIVEN: P gas = ? P total = torr P H2O = 42.2 torr WORK: P total = P gas + P H2O torr = P H torr P gas = 700. torr b A gas is collected over water at a temp of 35.0°C when the barometric pressure is torr. What is the partial pressure of the dry gas? Look up water-vapor pressure on p.899 for 35.0°C. Sig Figs: Round to least number of decimal places. D. Daltons Law The total pressure in the collection bottle is equal to barometric pressure and is a mixture of the gas and water vapor.

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