Gases AP Chemistry Mr. G

All matter follows the KMT: Kinetic Molecular Theory KMT- the tiny particles in all forms of matter are in constant motion. (Kinetic Energy) The Avg. Velocity of the particles depends on the temperature of the gas. (The hotter the gas, the faster its particles vibrate, colder gas particles vibrate _____.

KMT for gas behavior KMT – as it applies to gases: 1)A gas is composed of particles so tiny, that they have zero volume. (NOT REALLY!) 2) All gas particles have zero attractive or repulsive forces on each other. (NOT REALLY!) 3)All gas particles travel in straight lines, until they collide with each other or the walls of their containers. 4) All collisions are perfectly elastic, that is during a collision, kinetic energy is transferred without loss from one particle to another.

Real vs. Ideal Real Gases- Do NOT follow KMT, because real gases: 1) Particles have volume 2) Particles have some attractive forces (Intermolecular Forces) Gases deviate most from ideal behavior at ______ temperatures and _______ pressures.

Real Gas behavior

Allotropes-different forms of the same element, in the same physical state. Solid Carbon: Coal diamondgraphite C 60 (buckyballs) Amorphoustetrahedral hexagonal sheets Soccer ball shape (Random)networknetwork network

Allotropes-different forms of the same element, in the same physical state. Oxygen gas: O 2 O 3 diatomic oxygenozone

Air Composition Air is approx.: 77% N 2 (inert) 21% O 2 1% Ar Rest is all other gases

Physical Properties of Gases Expansion/Compression- an increase or decrease to the volume of a gas in a container. Fluidity- the ability to flow. Viscosity- the resistance of a liquid to flow. Diffusion- the spontaneous mixing of gases in the same container. Effusion- the spontaneous escaping of a gas from its container through a pinhole opening.

Gas Pressure Gas Pressure- the force exerted by a gas per unit surface area. Pressure = force / area Barometer = an instrument which measures atmospheric pressure. Draw a barometer on the board

Torricelli’s Barometer The height of mercury in Torricelli’s Barometer = ________ mm Hg 1.00 atmosphere = 760 mm Hg = 760 Torricelli = 14.7 PSI = KPa

Figure 5-2 p191

Manometer-measures pressure of a gas sample. Draw closed-ended Manometer

Pressure Conversions 1 atm = 760 mmHg = 760 torr = 14.7 PSI = Kpa 926 mmHg = ____ atm = ____ Kpa = ___ PSI = ___torr 15.7 PSI = ___ torr = ___mmHg = ___ Kpa = ___ atm 765 torr = ___ atm = ___PSI = ___Kpa = ____ mmHg

Volume Conversions

1 Liter = 1 dm 3 = 1000 mL = 1000 cm 3 = 1000cc 855 mL = ____ cm 3 = ____L = ____ dm 3 = ___ cc 1.85 L = ___ mL = ___ dm 3 = ___ cc = ___ cm 3 68 cm 3 = ___ mL = ___ dm 3 = ___ L = ____cc = ____m 3

Temperature Conversions Kelvin = Celcius o C = ________ K295 K = ______ o C 384 K = _________- 73 o C = _____K

Van der Waals Equation: a = IMF correction, b = volume correction Ideal Gas Law: PV = nRT R= l. atm / mol. K P = Press.(atm), V= vol.(L), n = mol, T = temp.(K) van der Waals Coefficients Gasa (Pa m 3 )b(m 3 /mol) Helium3.46 x x Neon2.12 x x Hydrogen2.45 x x Carbon dioxide3.96 x x Water vapor5.47 x x 10 -6

8.45 liters of N 2 gas exert 1.53 atm. of pressure at 45 0 C. How many moles of N 2 does the gas contain? 817 mL of O 2 gas at 95 0 C contain 7.35 grams of O 2. What is the pressure of the gas?

1.57 moles of Ar gas exert KPa in a bottle at 298 Kelvin. What is the volume of the bottle? How many grams are in a sample of CO 2 gas which occupies 655 ml at 55 0 C and exerts 846 torr of pressure?

Stoichiometry w/ ideal gas: Hydrogen peroxide decomposes to water and oxygen gas according to the following balanced equation: 2 H 2 O 2 (aq)  2 H 2 O(l) + O 2 (g) mL of 0.388M H 2 O 2 decomposes. What volume of oxygen forms at 25 o C and 795 torr?

Avogadro’s Law:

Combined Gas Laws- used when there is a change to PV or T: P 1 V 1 = P 2 V 2 Boyle’s Law Combined Gas Law P 1 V 1 = P 2 V 2 V 1 = V 2 Charles’ Law T 1 T 2 T 1 T 2 P 1 = P 2 Gay-Lussac Law T 1 T 2

355 mL of Ne gas are at 355 K and exert 2.35 atm of pressure. What pressure will it exert at 288 K and 368 mL?

A 1.25 dm 3 balloon exerts 795 torr. It then expands to 1.85 dm 3. What is the final pressure?(Assume constant temperature)

A steel tank of air exerts 395KPa at 25 o C. At what temperature does it exert 462KPa?

A piston contains 5.75 Liters of oxygen gas at 25 o C. What volume will it occupy at -36 o C?

85.5 mL of CO 2 gas are at STP. What pressure will it exert at 100. o C and compressed to 50.0 mL?

A sample of He at 38 o C, is heated to 95 o C and now occupies 75.0mL. What was the original volume? Identify the gas law:

Dalton’s Law of Partial Pressures-if different gases are mixed together, the total pressure of the mixture equals the sum of the partial pressures. Dalton’s Law: P total = P 1 + P 2 + P 3 …. Partial Pressure- the pressure exerted by an individual gas in a mixture, as if it were the only gas in the container.

A gas mixture the following partial pressures: 1.00 atm Ar, 3.00 atm Kr, 2.00 atm CO 2. What is the total pressure? What gas is present in the least and greatest amount? What is the mole fraction of each?

Wet Gas- A gas collected by bubbling through water. A wet gas is not pure, it contains water vapor, it is a gas mixture. The following picture shows how to collect a wet gas in the lab:

A sample of O 2 is collected over water. The total pressure of the wet O 2 is 785 torr. What is the pressure of the dry O 2 ?(VP H 2 O = 24 torr) What is the mole fraction of the O 2 ?

How many grams N 2 are in 425 mL sample at 298K at 772 torr collected over water?

According to KMT, KE of gas particles  T kelvin So, the KE of a gas particle: KE = ½ MV 2 KE of 1 mole of gas KE = 3/2 nRT (R= J/mol. K) Find the KE of a CH 4 gas molecule 298 K. Find the total KE of 78.2 grams of CH 4 at 298K

List each gas particle by increasing average KE, mass and velocity: N 2, NH 3, CH 4, O 2

Compare the relative rates of diffusion of carbon dioxide and nitrogen gas

Find the root-mean square velocity of carbon dioxide and nitrogen. Compare their  rms.

Compare the relative rates of effusion of helium and sulfur hexafluoride gases

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