Chapter 5 Note Guide

AP CHEMISTRY NAME: PERIOD: DATE: CHAPTER 5 NOTE GUIDE HW: # 8, 11, 12, 6,19,21,22,25,27,29,31,36,37,40,43,46,49,54,55,58,60,61,64,67,69,71,73,79, 82,85,92,100,104,106,114,118

PROPERTIES OF GASES . Relatively few substances exist in the gaseous state

. A gas uniformly fills a container

. It is easily compressed

. Mixes completely with any other gas

. Exert pressure on its surroundings

Atmospheric pressure-  Results from the mass of the air being pulled toward the center of the earth by gravity

 Varies with altitude. The higher you go, the smaller the mass of air pushing down on you = lower pressure

 At sea level, air pressure is measured as

760 mmHg or 760 Torr

1 AP CHEMISTRY NAME: PERIOD: DATE: How do we measure atmospheric pressure?

Barometer

. invented in 1643 by Evangelista Torricelli

. filled a glass tube with mercury and placed it into a pan of mercury

. a large amount of mercury remained up in the tube- he measured the height of this column in mmHg to find the atmospheric pressure at sea level = 760 mmHg

EQUIVALENT UNITS OF PRESSURE

SI unit – Pascals

______Pascals = ______kPa =______Atmospheres=______Torr =______mmHg=______inHg=______psi

2 AP CHEMISTRY NAME: PERIOD: DATE:

GAS LAWS

BOYLE’s LAW

 Pressure and volume are inversely proportional when temperature is held constant

 PV = k

 P1V1 = P2V2

Ex. A gas that has a pressure of 1.3 atm occupies a volume of 27L. What volume will the gas occupy if the pressure is increased to 3.9 atm at constant temperature?

3 AP CHEMISTRY NAME: PERIOD: DATE: CHARLES’ LAW

 When held at a constant pressure, the volume of a gas will increase directly with temperature

 V = bT

 V1/T1 = V2/T2

Ex. A gas at 30C and 1 atm of pressure occupies a volume of 0.842 L. What volume will the gas occupy at 60C and 1 atm?

AVOGADRO’s LAW  Equal volumes of gas at the same temperature and pressure contain the same number of atoms.

 V = an

 So, at a constant temperature and pressure, the number of moles of gas is directly proportional to the volume of gas.

 V1/n1 = V2/n2

 Most importantly, At STP (1 atmosphere of pressure and 0ºC)

1 mole of gas = 22.4L

IDEAL GAS LAW  Combines Boyle’s law, Charles’ law and Avogadro’s law into a law that allows variable temperature, pressure, number of moles and volume.

PV = nRT

Where R = the universal gas constant

R = .0821 L atm/ mol K or R = 8.315 L KPa/ K mol

5 AP CHEMISTRY NAME: PERIOD: DATE: Ex. A sample containing 0.614 moles of a gas at 12C occupies a volume of 12.9 L. What pressure does the gas exert?

THE COMBINED GAS LAW First condition variables: P1V1 = nR T1 Second condition variables: P2V2 = nR T2

Assuming a constant number of moles of gas in a closed system:

P1V1 / T1 = P2V2 / T2

PRACTICE PROBLEMS

1. A diver at a depth of 100 ft (pressure is approximately 3 atm) exhales a small bubble of air with a volume equal to 100 mL. What will the volume of the bubble be when he reaches the surface? Assume that the temperature remains constant. LAW USED: ______

2.A sample tube containing 103.6 mL of CO gas at 20.6 torr is connected to an evacuated 1.13 liter flask. What will be the pressure when the CO is allowed into the flask? LAW USED: ______

3.An 11.2L sample of a gas is determined to contain 0.50 moles of N2. At the same temperature and pressure, how many moles of gas would there be in a 20 L sample? LAW USED: ______

4.A weather balloon is filled with 0.295 m3 of helium on the ground at 18C and 756 torr. What will the volume of the balloon be at an altitude of 10 km where the temperature is -48C and the pressure is 0.14atm? LAW USED: ______

8 AP CHEMISTRY NAME: PERIOD: DATE: 5.A vacuum line used in a research lab has a volume of 1.103 L. The temperature in the lab is 23.7C and the vacuum line is evacuated to a pressure of 1x10-6 torr. How many gas molecules (atoms) remain? LAW USED: ______

IDEAL GAS LAW SUBSTITUTIONS

Solving for density:

9 AP CHEMISTRY NAME: PERIOD: DATE: Solving for molar mass:

DUMAS METHOD After measuring the density of a gas (by accurately weighing a known volume of gas) at a known temperature and pressure, its molar mass may be determined as follows:

MM = dRT / P

The density of a gas measured at 1.50 atm and 27C is 1.95 g/L. What is the molar mass of the gas?

DALTON’s LAW of PARTIAL PRESSURES For a mixture of gases in a closed container, the total pressure exerted is the sum of the pressures that each gas would exert if it were alone.

Ex. A mixture of 2.0 L of He @ 46C and 1.2 atm is added to a vessel that contains 4.5 L of N2 at STP. What is the total pressure and the partial pressure of each gas at STP?

Ex. O2 is collected over water at 25.0ºC, what is the pressure of the dry gas if the atmospheric pressure was 762.0 mmHg?

11 AP CHEMISTRY NAME: PERIOD: DATE: MOLE FRACTION

 The ratio of the number of moles of an individual gas to the total number of moles in the mixture.

 = ___moles of individual gas__ Total moles of gas in mixture

The mole fraction is directly related to the partial pressure of each gas.

 = __partial pressure of individual gas__ Total pressure of gases

Ex. What is the mole fraction of He and N2 gas in the problem above?

12 AP CHEMISTRY NAME: PERIOD: DATE: STOICHIOMETRIC CALCULATIONS INVOLVING GAS LAWS

MOLAR VOLUME = 22.4 L/ mole at STP

1) A sample containing 15.0 g of dry ice (CO2(s)) is put into a balloon and allowed to sublime into

CO2(g). How big will the balloon be, at 22C and 1.04 atm. CO2 (g)  molecular weight  moles CO2 (g)  ideal gas law  volume CO2

2) 0.500 L of H2(g) are reacted with 0.600 L of O2(g) at STP to form water vapor. What volume will the

H2O occupy at 1.00 atm and 350C.

13 AP CHEMISTRY NAME: PERIOD: DATE: LIMITING REAGENT PROBLEM! Moles H2O from H2 =

Moles H2O from O2 =

Moles H2O formed  ideal gas law  volume of product

14 AP CHEMISTRY NAME: PERIOD: DATE: THE KINETIC MOLECULAR THEORY OF GASES

 Ideal gas behavior is most closely approached when the pressure is less than 1 atm and temperature is maximized. Real gases do not assume such behavior.

 To predict ideal gas behavior using a model, some assumptions must be made.

4 POSTULATES of the KINETIC MOLECULAR THEORY

1. The volume of the individual particles is assumed to be negligible. 2. The particles are in constant motion and the collisions of the gas with the walls of the container cause pressure. 3. The particles are assumed to exert no attractive or repulsive forces on each other. 4. The average kinetic energy of a collection of gas particles is assumed to be directly proportional to the Kelvin temperature.

15 AP CHEMISTRY NAME: PERIOD: DATE: AVERAGE KINETIC ENERGY FOR A MOLE OF GAS PARTICLES:

(KE)average = 3/2 RT

 Temperature is a measure of the average kinetic energy of a gas.

ROOT MEAN SQUARE VELOCITY

rms = square root (3RT/M)

M = molar mass in kg/mol T = Kelvin temperature R = 8.315 kg m 2 /s 2 Kmol

Ex. Calculate the rms velocity for the atoms in a sample of oxygen gas at 0ºC and 300ºC.

 Speed is related to the size and mass of the atom of molecule

 A probability plot can be drawn for gases at certain temperatures. Not every atom or molecule will be travelling at the same speed. A distribution of speeds exists. Called the Maxwell-Boltzman distribution.

GRAHAM’s LAW of EFFUSION/ DIFFUSION

17 AP CHEMISTRY NAME: PERIOD: DATE:  The velocity of a gas is inversely proportional to its molar mass

EFFUSION: Passage of a gas through an orifice into an evacuated chamber

DIFFUSION:

Mixing of gases

Ex. How many times faster than NO2 would He gas effuse?

Ex. What are the relative rates of diffusion for methane and oxygen?

REAL GAS BEHAVIOR

 Real gases exhibit behavior of ideal gases at high temperatures and low pressures? Why?

Particle interactions have been minimized as molecules are further apart and moving with a higher kinetic energy.

Van Der Waals relationship: 1.considers the volume of the gas molecules

2.attractions between molecules (London dispersion forces) are also considered a.higher concentration of gases/ more of a correction factor because there is more chance that the molecules would interact. b.These interactions all lead to a decrease in pressure.

19 AP CHEMISTRY NAME: PERIOD: DATE: Interactions between particles lessen their effect on the container walls thereby decreasing the pressure.

VAN DER WAALS EQUATION:

(P + a n2/V2)(V - nb) = nRT

Ex. Calculate the pressure exerted by 0.300 mole of He in a 0.2000L container at -25.0ºC. a. Using the ideal gas law

b. Using van der Waal’s equation

ATMOSPHERIC CHEMISTRY Read and complete on your own.

1. The atmosphere is composed of ____%N2, ____%O2, ____%Ar, ____%CO2 along with other trace gases.

Smog reactions

1. N2(g) + O2(g)

2. NO (g) + O2(g) 

3. NO2(g) + radiant energy 

4. O(g)+O2(g)

Acid rain reactions 1. NO2(g) + H2O (l) 

2. SO2(g) + O2(g) 

3. SO3(g) + H2O(l)