III Ideal Gas Law A Avogadros Principle Equal

III. Ideal Gas Law

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

A. Ideal Gas Law Merge the Combined Gas Law with Avogadro’s Principle: PV V k =R n. T T n UNIVERSAL GAS CONSTANT R=0. 0821 L atm/mol K 3 R=8. 315 dm k. Pa/mol K You don’t need to memorize these values!

A. Ideal Gas Law PV=n. RT UNIVERSAL GAS CONSTANT R=0. 0821 L atm/mol K 3 R=8. 315 dm k. Pa/mol K You don’t need to memorize these values!

C. Ideal Gas Law Problems Calculate the pressure in atmospheres of 0. 412 mol of He at 16°C & occupying 3. 25 L. GIVEN: WORK: P = ? atm PV = n. RT n = 0. 412 mol P(3. 25)=(0. 412)(0. 0821)(289) mol L atm/mol K T = 16°C = 289 K K L V = 3. 25 L P = 3. 01 atm R= 0. 0821 L atm/mol K

C. Ideal Gas Law Problems Find the volume of 85 g of O 2 at 25°C and 104. 5 k. Pa. GIVEN: WORK: V=? 85 g 1 mol = 2. 7 mol n = 85 g = 2. 7 mol 32. 00 g T = 25°C = 298 K PV = n. RT P = 104. 5 k. Pa (104. 5)V=(2. 7) (8. 315) (298) k. Pa mol dm 3 k. Pa/mol K R = 8. 315 V = 64 dm 3 k. Pa/mol K

D. Dalton’s Law The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases. Ptotal = P 1 + P 2 +. . . When a H 2 gas is collected by water displacement, the gas in the collection bottle is actually a mixture of H 2 and water vapor.

D. Dalton’s Law Hydrogen gas is collected over water at 22. 5°C. Find the pressure of the dry gas if the atmospheric pressure is 94. 4 k. Pa. The total pressure in the collection bottle is equal to atmospheric pressure and is a mixture of H 2 and water vapor. GIVEN: PH 2 = ? Ptotal = 94. 4 k. Pa PH 2 O = 2. 72 k. Pa Look up water-vapor pressure on p. 899 for 22. 5°C. WORK: Ptotal = PH 2 + PH 2 O 94. 4 k. Pa = PH 2 + 2. 72 k. Pa PH 2 = 91. 7 k. Pa Sig Figs: Round to least number of decimal places.

D. Dalton’s Law A gas is collected over water at a temp of 35. 0°C when the barometric pressure is 742. 0 torr. What is the partial pressure of the dry gas? The total pressure in the collection bottle is equal to barometric pressure and is a mixture of the “gas” and water vapor. GIVEN: Pgas = ? Ptotal = 742. 0 torr PH 2 O = 42. 2 torr Look up water-vapor pressure on p. 899 for 35. 0°C. WORK: Ptotal = Pgas + PH 2 O 742. 0 torr = PH 2 + 42. 2 torr Pgas = 699. 8 torr Sig Figs: Round to least number of decimal places.

E. Graham’s Law Diffusion Spreading of gas molecules throughout a container until evenly distributed. Effusion Passing of gas molecules through a tiny opening in a container