Honors Chemistry Chapter 12 Gas Laws

12.1 Kinetic Molecular Theory Describes the behavior of matter in terms of particles in motion Makes several assumptions about the size, motion, and energy of gas particles

Assumptions of the Kinetic Molecular Theory Gases consist of small particles Gases take up little volume relative to the volume of empty space around them so size of individual particles is zero

Gas particles move in constant, random straight lines until they collide with other particles or with the walls of the container Collisions are elastic – Collisions cause gas pressure -

Gas particles do not attract or repel each other The average kinetic energy of gas particles is directly proportional to the KELVIN temperature of the gas

Meaning of temperature – Kelvin temperature is directly proportional to the average kinetic energy of the gas particles Relationship between Pressure and Temperature – gas pressure increases as the temperature increases because the particles speed up Relationship between Volume and Temperature – volume of a gas increases with temperature because the particles speed up

12.2 Properties of Gases Gases can be compressed and can expand Why are gases compressible but solids and liquids are not?

When a person collides with an inflated airbag, the compression of the gas absorbs the energy of the impact.

Gases diffuse and effuse Diffusion = gas particles move from an area of high concentration to low concentration Ex Effusion = gas particles escape through tiny openings

Bromine vapor is diffusing upward through the air in a graduated cylinder. The diffusion of one substance through another is a relatively slow process. a) Bromine vapor is diffusing upward through the air in a graduated cylinder. b) After several hours, bromine vapors are near the top of the cylinder. Predicting What will happen as the bromine continues to diffuse?

After several hours, the bromine has diffused almost to the top of the cylinder. The diffusion of one substance through another is a relatively slow process. a) Bromine vapor is diffusing upward through the air in a graduated cylinder. b) After several hours, bromine vapors are near the top of the cylinder. Predicting What will happen as the bromine continues to diffuse?

Grahm’s Law - states that the rate of effusion of a gas is inversely proportional to the square root of the gas’s molar mass. This law can also be applied to the diffusion of gases. Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass. Helium filled balloon deflates faster than air filled balloon

Ammonia has a molar mass of 17 Ammonia has a molar mass of 17.0 g/mol, hydrogen chloride has a molar mass of 36.5 g/mol. What is the ratio of their diffusion rates?

What is the molar mass of a gas that takes four times as long to effuse as hydrogen?

Gases exert pressure What causes gas pressure? What are three factors that effect gas pressure?

Units of pressure: 1 standard atmosphere = 1.000 atm = 760.0 mm Hg = 760.0 torr = 101.3 kPa

Dalton’s law of partial pressures: Total pressure of a mixture of gasses is equal to the sum of the pressures of all of the gasses in the mixture P1 + P2 + P3…=Ptotal

A mixture of oxygen, carbon dioxide, and nitrogen has a total pressure of 0.97 atm. What is the partial pressure of O2 if the partial pressure of CO2 is 0.70 atm and the partial pressure of N2 is 12.16 kPa?

Variables effecting a gas: Amount of gas Moles Temperature Kelvin = Celsius + 273 Volume L mL Pressure kPa atm mmHg

Amount of Gas You can use kinetic theory to predict and explain how gases will respond to a change of conditions. If you inflate an air raft, for example, the pressure inside the raft will increase. Why?

If the gas pressure increases until it exceeds the strength of an enclosed, rigid container, the container will burst. When a gas is pumped into a closed rigid container, the pressure increases as more particles are added. If the number of particles is doubled, the pressure will double. Predicting What would happen to the pressure in the container if the number of particles were tripled? If the number of particles were cut in half?

Temperature An increase in the temperature of an enclosed gas causes an increase in its pressure. Why?

When the Kelvin temperature of the enclosed gas doubles, the pressure of the enclosed gas doubles. An increase in temperature causes an increase in the pressure of an enclosed gas. The container can explode if there is too great an increase in the pressure.

Volume You can raise the pressure exerted by a contained gas by reducing its volume. The more a gas is compressed, the greater is the pressure that the gas exerts inside the container. Why?

When the volume of the container is halved, the pressure the gas exerts is doubled. A piston can be used to force a gas in a cylinder into a smaller volume. When the volume is decreased, the pressure the gas exerts is increased. Interpreting Diagrams What happens to the gas pressure when the volume is reduced from 1 L to 0.5 L?

12.3 The Gas Laws

Boyles Law TEMPERATURE & AMOUNT CONSTANT Pressure and volume are inversely related P1 x V1 = P2 x V2 Relate to KMT

A diver blows a 0. 75 L air bubble 10 m under water A diver blows a 0.75 L air bubble 10 m under water. As it rises to the surface, the pressure goes from 2.25 atm to 1.03 atm. What ill be the volume of the air in the bubble at the surface?

Charles’s Law PRESSURE AND AMOUNT CONSTANT Flexible container Volume and temperature are directly related Temperature must be in K! Relate to KMT

A helium balloon in a closed car occupies a volume of 2. 32 L at 40 A helium balloon in a closed car occupies a volume of 2.32 L at 40.0 oC. If the car is parked on a hot day and the temperature inside rises to 75.0 oC what is the new volume of the balloon?

Gay-Lussac’s Law VOLUME AND AMOUNT CONSTANT Pressure and Temperature are directly related Temperature must be in K! Relate to KMT

Helium gas in a 2. 00 L cylinder is under 1. 12 atm pressure. At 36 Helium gas in a 2.00 L cylinder is under 1.12 atm pressure. At 36.5 oC that same gas sample has a pressure of 2.56 atm. What was the initial temperature of the gas in the cylinder in degrees Celsius?

Avagadro’s Law PRESSURE AND TEMPERATURE CONSTANT Volume and amount of gas (moles) are directly related

Volume and Moles: Avogadro’s Law

If 46. 2 g of oxygen gas occupies a volume of 80 If 46.2 g of oxygen gas occupies a volume of 80.0 L at a constant temperature and pressure, what volume will 10.0 g of oxygen occupy under the same conditions?

Combined Gas Law AMOUNT OF GAS CONSTANT

A sample of air in a syringe exerts a pressure of 1.02 atm at 22.0 oC. The syringe is placed in a boiling water bath at 100.0 oC. The pressure is increased to 1.23 atm by pushing the plunger in, which reduces the volume to 0.224 mL. What was the initial volume?

The Ideal Gas Law Relates number of particles, pressure, temperature, and volume Talk about 1st part of paragraph

The Ideal Gas Law PV = nRT R = 8.31 L*kPa/mol*K R = 0.0821 L*atm/mol*K Units for each variable

Ideal Gas Law: Determine the volume of a tank that containing 93 Ideal Gas Law: Determine the volume of a tank that containing 93.0 g of carbon dioxide, and has a pressure of 800. mm Hg at 22.0⁰ C.

What is the volume of one mole of gas at STP? (STP = )

How many moles of a gas are in 2.50 L of gas at STP?

If the density of a gas is 1. 2 g/L at 745 torr and 20 If the density of a gas is 1.2 g/L at 745 torr and 20.0⁰ C, what is its molar mass?

Gas Stoichiometry When gases react, the coefficients in the balanced chemical equation represents both molar amounts and relative volumes 2H2(g) + 2O2(g)  2H2O(g)

Volume – Volume problems What volume of oxygen gas is needed for the complete combustion of 4.00 L of methane gas? CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)

What volume of carbon dioxide gas can be made from 2.36 L of methane?

Volume – Mass problems If 5.00 L of nitrogen reacts completely with hydrogen at a pressure of 3.00 atm and a temperature of 298 K, how much ammonia, in grams, is produced? N2(g) + 3H2(g)  2NH3(g)

NH4NO3(s)  N2O(g) + 2H2O(g) What mass of solid ammonium nitrate must be used to obtain 0.100 L of dinitrogen oxide gas at STP?

Real vs. Ideal Gas Ideal gases follow the assumptions of the kinetic-molecular theory Particles take up no space Experience no intermolecular forces Not attracted to or repelled by the walls of their container Follow the gas laws under all temperatures and pressures

Real Gases Gases do not behave ideally under conditions of high pressure and low temperature. Why?

Real Gases At high pressure the volume is decreased Molecule volumes become important Attractions become important