Chem unit 12 presentation

How do Gases

Behave?Chem Unit 12

Main Ideas

For a fixed amount of gas, a change in one variable – pressure, temperature, or volume – affects the other two.

The ideal gas law relates the number of particles to pressure, temperature, and volume.

When gases react, the coefficients in the balanced chemical equation represent both molar amounts and relative amounts.

The Gas Laws

12.1

The Gas Laws: Objectives

State the relationship among pressure, temperature and volume of a constant amount of gas.

Apply the gas laws to problems involving the pressure, temperature, and volume of a constant amount of gas.

Pressure Units

Pressure Units:

1 atm = 1 atmosphere

1 atm = 760 Torr (short for Toricelli)

1 atm = 760 mm Hg

1 atm = 101,325 Pa (short for Pascal)

1 atm = 101 kPa (kilopascal)

Boyles Law

Robert Boyle (1629-1691), an Irish chemist, described this relationship between pressure and the volume of a gas.

How are pressure and volume related?As volume goes down, pressure

goes up. Inverse relationshipExample:

Boyles Law

Boyle’s law states that the volume of a fixed amount of gas held at a constant temperature varies inversely with the pressure.

Formula: P1V1 = P2V2

Practice Problem #1

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 will be the volume of air in the bubble at the surface?

1.6 L

Charles Law

Jacques Charles (1746-1823), a French physicist, studied the relationship between volume and temperature.

How are temperature and volume related?As temperature goes up, volume

goes up. Direct relationshipExample:

Charles Law

Charles’s law states that the volume of a given amount of gas is directly proportional to its Kelvin temperature at constant pressure.

Formula: Temperature in KelvinA temperature of 0 K corresponds to 0

ml, and doubling the temperature doubles the volume. Zero on the Kelvin scale is also known as absolute zero.

This is the lowest possible theoretical temperature.

Practice Problem #2

A helium balloon in a closed car occupies a volume of 2.32 L at 40.0°C. If the car is parked on a hot day and the temperature inside rises to 75.0°C, what is the new volume of the balloon, assuming the pressure remains constant?

2.58 L

Lussac’s Law

Joseph Lussac (1778-1850), found that a direct pressure of a fixed amount of gas varies directly with the Kelvin temperature when the volume remains constant.

How are temperature and pressure related?As temperature goes up, pressure

goes up. Direct relationshipExample:

Lussac’s Law

Lussac’s Law states that the pressure of a fixed amount of gas varies directly with the Kelvin temperature when the volume remains constant.

Formula:

Practice Problem #3

The pressure of the oxygen gas inside a canister is 5.00 atm at 25.0°C. The canister is located at a camp high on Mount Everest. If the temperature there falls to -10.0°C, what is the new pressure inside the canister?

4.41 L

Combined Gas Law

The Combined Gas Law states the relationship among pressure, temperature, and volume of a fixed amount of gas. The relationships are the same as the other laws but combined into one mathematical statement.

Formula:

Practice Problem #4

A gas at 110kPa and 30.0°C fills a flexible container with an initial volume of 2.00 L. If the temperature is raised to 80.0°C and the pressure increases to 440 kPa, what is the new volume?

0.58 L

Homework

CALM: 5 questions

P443 #1,2; P446 #4-6

P448 #8-10; P450 #11-13

P451 #14-18

The Ideal Gas Law

12.2

The Ideal Gas Law: Objectives

Relate number of particles and volume using Avogadro’s principle.

Relate the amount of gas present to its pressure, temperature, and volume using the ideal gas law.

Compare the properties of real and ideal gases.

Avogadro’s Principle

Avogadro’s Principle states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.

The size of the molecules do not matter; therefore the identity of the gas does not matter.

Example:

Molar Volume

Molar Volume of a gas is the volume that 1 mol occupies at 0.00° C and 1 atm pressure.

STP: The conditions of 0.00°C and 1.00 atm are known as standard temperature and pressure.

1 mol of gas at STP = 22.4 L

Practice Problem #5

How many moles are in a sample of gas that has a volume of 3.72 L at STP?

1.66 L

Practice Problem #6

The main component of natural gas used for home heating and cooking is methane (CH4). Calculate the volume that 2.00 Kg of methane gas will occupy at STP.

2.80x103 L

Ideal Gas Law

Avogadro’s principle, Boyle’s law, Charles’s law and Lussac’s law can all be combined into a single mathematical statement that describes the relationship among pressure, volume, temperature and number of moles of a gas.

Constant

Ideal Gas Law

Since ideal gases react the same no matter their identity, every gas has the same constant when using the Ideal Gas Law.

 0.08206 (L atm)/(mol K)

Practice Problem #7

Calculate the number of moles of ammonia gas (NH3) contained in a 3.0 L vessel at 3.00 x 102 K with a pressure of 1.50 atm.

0.18 mol

Real vs. Ideal Gases

Ideal gases follow the assumptions of the kinetic molecular theory (KMT). Assumptions:

1.An ideal gas is one whose particles do not take up space.Gas molecules do not have volume;

their movement creates volume.

Real vs. Ideal Gases

Ideal gases follow the assumptions of the kinetic molecular theory (KMT). Assumptions:

2.Ideal gases do not experience intermolecular attractive forces.Gas molecules are too far apart to

attract or repel each other.

Real vs. Ideal Gases

Ideal gases follow the assumptions of the kinetic molecular theory (KMT). Assumptions:

3.Ideal gas particles are in constant, random motion and collide with each other and the walls of the container. Collisions of the molecules are

elastic and cause pressure.

Real vs. Ideal Gases

In reality, no gas is truly ideal. Most gases behave like ideal gases at a wide range of temperatures and pressures. Under the right conditions, calculations made using the ideal gas law closely approximate experimental measurements.

Real vs. Ideal Gases

When do real gases not behave as ideal gases?

1. Low temperatures Gas molecules do not have the

kinetic energy they usually do and do not move as fast. Because they are moving slowly, attractive forces can change the way they behave.

Real vs. Ideal Gases

When do real gases not behave as ideal gases?

2. High pressuresGas molecules are crowded and

their volume becomes significant to the overall volume of the container.

Gas Stoichiometr

y13.3

Gas Stoichiometry: Objectives

Determine volume ratios for gaseous reactants and products by using coefficients from chemical equations.

Apply gas laws to calculate amounts of gaseous reactants and products in a chemical reaction.

Gas Stoichiometry

Stoichiometry of reactions involving gases often give pressure, volume and/or temperature in order to find moles.

The “core” process of the stoichiometry remains the same.

Practice Problem #8

What volume of oxygen gas is needed for the complete combustion of 4.00L of propane gas (C3H8)? Assume that pressure and temperature remain constant.

20.0 L O2; because moles and volume are directly related, volume can be used with the mole ratios.

Practice Problem #9

Ammonia is synthesized from hydrogen and nitrogen.

N2(g) + 3H2(g) 2NH3(g)

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?

21.0 g NH3

Practice Problem #10

What volume of H2O(g) measured at STP is produced by the combustion of 5.73 g of natural gas (CH4) according to the following equation?

CH4(g) + 2O2(g) CO2(g)+2H2O(g)

16 L

Practice Problem #11

Calcium hydride combines with water according to the equation

CaH2(s) + 2H2O(l) 2H2(g) + Ca(OH)2(s)

Beginning with 84.0 g of CaH2 and 36.0 g of H2O, what volume of H2 will be produced at 273 K and a pressure of 1609 torr?

Practice Problem #12

Ammonia is synthesized from hydrogen and nitrogen.

N2(g) + 3H2(g) -> 2NH3(g)

You have 15.0g of N2 and 5.0g of H2 at STP. How many grams of NH3 can be produced and what is the mass of the excess reactant?

Accumulating Content

12.4

Accumulating Content: Objectives

Apply knowledge and skills from previous units to content learned in this unit.

Accumulating Content Paper

Write a one page paper (single spaced) about how chemistry and gases are related.

Ideas:

Medical: hyperbaric chamber, ozone, anesthetic gases

Ecological: greenhouse gases, gas pollution

History: Haber, chemical warfare, pneumatic chemists