Gases Ch.10 and 11

Kinetic-Molecular Theory 1.Gases consist of very small particles that are far apart Most particles are molecules Volume of particles = 0 because total volume of gas is very large

Kinetic-Molecular Theory 2.Collisions are “elastic” – no net loss of total energy 3.Particles in constant, rapid, random motion Fill containers easily, overcome attractive forces between them

Kinetic-Molecular Theory 4.Particles have no attraction or repulsion to each other 5.Temperature of gas depends on average kinetic energy of particles Kelvin = o C Inc. Temp. = Inc. Energy Dec. Temp = Dec. Energy

Kinetic-Molecular Theory Assumptions for IDEAL GASES (imaginary gases) Particles = 0 volume Particles = 0 volume No attraction between particles No attraction between particles Real gases HAVE volume and SOME attraction b/ particles

Properties of Gases Expansion – constant, random motion Fluidity – low attraction Low density – particles far apart Compressibility – easily change pressure and volume Diffusion – gases mix easily Effusion – pass through tiny openings

Measuring Gases

Pressure depends on temp. and volume Def: force per unit of area Def: force per unit of area Many units pg. 364 Many units pg atm = 760 mmHg = 760 torr = psi = 101,325 Pa = kPa Barometer – device used to measure atmospheric pressure (p. 363)

Examples 15.0 psi = ? atm 693 mmHg = ? Pascals

Dalton’s Law of Partial Pressure

Gas MIXTURES Each gas has partial pressure Dalton’s Law states: The sum of the partial pressures of all the gases in the mixture is equal to the total pressure of the mixture. P T = p a + p b + p c + …

Dalton’s Law If the atmospheric pressure is 767 mmHg and the partial pressures of nitrogen and oxygen are 604 mmHg and 162 mmHg, what is the partial pressure of argon?

Dalton’s Law What is the partial pressure of nitrogen in air if the total pressure is 1.5 atm and nitrogen makes up 15% of the air?

Dalton’s Law over Water p. 366 Gases are then mixed with H 2 O vapor P atm = P gas + P water P water varies with temp. (p. 859) Sample of N 2 gas was collected over water at 23.0 o C. What is the pressure of the N 2 if the atmospheric pressure is 785 mmHg?

Boyle’s Law

Pressure – Volume Relationship P and V are inversely proportional at constant temperature. P and V are inversely proportional at constant temperature. As one  the other .

Boyle’s Law P o V o = P n V n P o = original Pressure V o = original Volume P n = new Pressure V n = new Volume

Boyle’s Law A gas at 25 o C and 748 mmHg occupies 2.18 L. At 25 o C, what is the pressure, in Pa, if you decreased the volume to L?

Boyle’s Law A gas has a volume of L at 23 o C and 1.00 atm. What is the volume if you increased the pressure to 946 torr at 23 o C?

Charles’s Law

Volume – Temperature Relationship V and T are directly proportional at constant pressure V and T are directly proportional at constant pressure As one  the other  As one  the other  T is in KELVIN!! T is in KELVIN!!

Charles’s Law V o = V n T o T n V o = original Volume T o = original Temperature V n = new Volume T n = new Temperature

Charles’s Law A sample of gas at a constant pressure and –18 o C has a volume of 1.00L. What is the temperature if the volume is changed to.45L?

Gay-Lussac’s

Gay-Lussac’s Pressure – Temperature Relationship P and T are directly proportional at constant volume P and T are directly proportional at constant volume As one  the other  As one  the other  T is in KELVIN!! T is in KELVIN!!

Combined Gas Law At 15 o C a gas occupies.59 L at a pressure of 23 psi. What is the temperature if the volume was increased to 1.09 L and the pressure was 1.2 atm?

Combined Gas Law A gas cylinder at 20.0 o C is thrown into an incinerator where the temperature is o C. If the pressure was initially 1.0 atm, what pressure did it reach inside the incinerator? (assuming at constant V and did not explode)

Avogadro’s Law

Def: equal volumes of gases at same T and P contain equal # of molecules All gas particles so small ~ same size All gas particles so small ~ same size STP : Standard Temperature & Pressure 0 o C and 1 atm 0 o C and 1 atm At STP, 1 mole = 22.4 L At STP, 1 mole = 22.4 L

Gas Stoichiometry What volume of H 2 gas is produced from 3.9 g of NH 3, at STP? Need mol H 2  L H 2 gas Need mol H 2  L H 2 gas 2NH 3 (g)  3H 2 (g) + N 2 (g)

Gas Stoichiometry Xenon gas reacts w/ excess fluorine gas to produce Xenon hexafluoride. Need to produce 3.14 L XeF 6, how many L of fluorine do we need? Use Mole Ratios as VOLUME ratios Use Mole Ratios as VOLUME ratios

Ideal Gas Law

Give “instant” results Compares: P, V, T and n (moles) of ideal gases At normal conditions real gases ARE ideal gases At LOW temp. and HIGH pressure real gases ARE NOT ideal gases

Ideal Gas Law PV = nRT P = pressure in atm V = volume in L n = moles T = temp. in KELVIN!! R = ideal gas constant L atm/ mol K

Examples How many moles of gas at 100. o C does it take to fill a 1.00 L flask to a pressure of 22.1 psi?

Examples What is the volume occupied by 9.45 g of C 2 H 2 at STP?