Chem. Catalyst 7 - De La Salle High SchoolChem. Catalyst 7.1 List a few ... Combined Gas Law 5....

Gases

Mr. Shively

De La Salle High School

Chem. Catalyst 7.1

List a few physical properties of gases that you know from

previous science classes.

General Properties of Gases

Have indefinite shape and

volume

Have mass

Compressible

Pressure

Demonstration

What happened to the can?

Why do you think it happened?

Pressure Defined

Molecules are constantly moving and collide

with each other as well as other molecules

Collisions between gas molecules and walls of

container creates pressure.

forcepresssure

area

Barometer and Units of Pressure

Units of Pressure

1 atmosphere = 1 atm

1 atm = 760 mmHg

1 atm = 760 torr

1 atm = 101,325 Pa

1 atm = 101.325 kPa

Practice Pressure Conversions

A scientist measures three balloons to have the following

pressures. Calculate the pressure of each balloon in

atmospheres.

Balloon 1 = 801 mm Hg

Balloon 2 = 721 torr

Balloon 3 = 102,706 Pa

Manometer

A manometer is a device

used to calculate the

pressure of a gas by

comparing it to

atmospheric pressure

Manometer

Calculate the pressure of

the gas sample in the

manometer to the right in

atmospheres. Assume the

atmospheric pressure to be

769 mm Hg and the height

of the mercury column is

49 mm Hg.

Chem. Catalyst 7.2

What is pressure?

Name the device commonly used to measure atmospheric

pressure.

The current barometric pressure in Concord, CA is 30.12

in Hg. What is the pressure in atmospheres? (1 in = 2.54

cm)

Gas Laws

Gas laws are mathematical relationships between

properties of ideal gases.

1. Boyle’s Law

2. Charles’s Law

3. Gay-Lussac’s Law

4. Combined Gas Law

5. Avogadro’s Law

6. Ideal Gas Law

7. Dalton’s Law

8. Graham’s Law

Boyle’s Law

Pressure and volume are indirectly proportional

1 1 2 2PV PV

“An increase in

volume leads to a

decrease in pressure at

constant temperature.”

Boyle’s Law Practice Problem 1

A balloon with a volume of 1.00 L and a pressure of 1.00

atm is released into the atmosphere. What will the

volume of the balloon be at 3, 000 ft where the pressure

is 0.90 atm. Assume constant temperature.

Charles’s Law

Temperature and volume are

directly proportional

1 2

1 2

V V

T T

“An increase in

temperature leads to

an increase in

volume at constant

pressure.”

Charles’ Law Practice Problem 1

A closed container with a volume of 4.5 L and a

temperature of 28 oC is heated to 45 oC. Calculate the

volume of the closed container at this temperature.

Gay-Lussac’s Law

A quantity of gas in a steel container has a pressure of

760 torr at 25°C. What is the pressure in the container if

the temperature is increased to 50°C?

Combined Gas Law

The combined gas law relates initial conditions of

pressure, temperature and volume and final conditions of

pressure temperature and volume.

What happens to the combined

gas law,

When temperature is constant?

When pressure is constant?

When volume is constant?

Chem. Catalyst 7.3

Two balloons, one red and one blue, have a pressure of 760

torr and a volume of 1.4 L. The balloons both have an initial

temperature of 273 K. The volume of the red balloon is

increased until the pressure of the balloon is 710 torr.

The temperature of the blue balloon is increased to 352

K. Which balloon has a greater volume after the changes

have been made?

Avogadro’s Law

The volume of a gas is directly proportional to the

number of moles of gas at constant temperature and

pressure.

V1 V2

= n1 n2

Avogadro’s Law

A balloon that is not inflated but is full of air has a volume of

275 mL and contains 0.0120 mol of air. As shown in the

figure to the right, a piece of dry ice (solid CO2) weighing

1.00 g is placed in the balloon and the neck is tied. What is

the volume of the balloon after the dry ice has vaporized?

(Assume constant T and P.)

Avogadro’s Law and Combining Volumes

The volume of gas at constant T and P is directly

proportional to the number of moles of gas.

Combining Volumes Practice Problem #1

Nitrogen and hydrogen can be combined according to the

following equation:

N2 + 3 H2 2 NH3

If 3.0 L of nitrogen combine with 3.0 L of hydrogen, how

many L of ammonia are produced? Assume the

temperature and pressure are constant.

Molar Volume of a Gas

Molar volume of a gas

At STP(standard

temperature and

pressure) 1 mole of a gas

has a volume of 22.4 L

Conditions of STP

273 K or O0C

1 atm

Practice Problem

Calculate the number of moles of nitrogen gas and

methane gas (CH4) if each of the following samples are at

STP.

Calculate the mass of gas in each sample.

5.0 L of

N2 gas

5.0 L of

CH4 gas

Chem. Catalyst 7.3

Create a list of all the gas laws you have learned in this unit.

Write the formulas and corresponding names.

Gas Laws Mini Review (1 of 2)

A sample of gas in a closed container has a volume

of 125 mL and a pressure of 450 torr. Calculate the

new pressure if the volume of the gas is increased to

145 mL.

A balloon has a volume of 325 mL at 17oC. What is

the temperature in oC if the volume increases to

392 mL.

An aerosol spray can has gas under pressure of 1.25

atm at 25oC. The can explodes when the pressure

reaches 2.50 atm. At what temperature will this

happen?

390

torr

77 oC

596 K or

323 oC

Gas Laws Mini Review (2 of 2)

In the following table, indicate whether the pressure,

volume or temperature increases or decreases.

A balloon has a volume of 188 L and contains 8.40

moles of gas. How many moles of gas would be

needed to expand the balloon to 275 L? Assume the

same temperature and pressure in the balloon.

Experiment P V T

1

Increases Constant

2 Constant Decreases

3 Decreases constant

3.9 mol

Ideal Gas Law

Relates pressure, volume, number of moles and

temperature (in K) of an ideal gas

R is the ideal gas constant.

This equation can be used to solve for any of the four

variables as long as three are known.

UNITS for PV and T must be in atm, L and K.

=

Ideal Gas Law Practice Problem #1

A model blimp is filled with helium to a pressure of 760

mm Hg. The volume of the blimp is 5.00 L and the

temperature is 24 oC. How many moles of helium are in

the balloon?

Chem. Catalyst 7.4

What is the equation for the ideal gas law?

Calculate the pressure (in torr) exerted by 0.250 g of O2

in a 250 mL container at 29oC?

590 torr


Calculate the volume of a gas in liters if 1.50 moles of

the gas has a pressure of 0.985 atm at a temperature of

-6oC.

Ideal Gas Law Practice Problem 3

Calculate the number of grams of acetylene, C2H2 in a

30.0 L cylinder at a temperature of 20.0oC and a pressure

equal to 9,010 torr.


4.2 grams of a gas are added to an evacuated chamber

with a volume 2.0 L. Minutes later the pressure of the

chamber is determined to be 0.98 atm. The temperature

of the gas sample was also determined to be 0 0C. What

is the molar mass of the gas sample?

Gas Stoichiometry

Mass (g)

Given

Moles

Given

Particles

Given Molar Mass

(g/mol)

6.022x1023

(particles/mol)

Mass (g)

unknown

Moles

unknown

Particles

Unknown

Molar Mass

(g/mol)

6.022x1023

(particles/mol)

Volume of

Gas

1 mol gas = 22.4 L at STP

Volume of

Gas

1 mol gas = 22.4 L at STP

Mole ratio

PV=nRT

PV=nRT

Gas Stoichiometry Practice Problem #1

Calculate the mass of NO2 gas produced if 5.00 L of

nitrogen gas at 1.00 atm of pressure and 0oC react with

excess oxygen gas.

N2 (g) + 2 O2 (g) 2 NO2 (g)


Quicklime (CaO) is produced by the thermal

decomposition of calcium carbonate (CaCO3). Calculate

the volume of CO2 at STP produced by the

decomposition of 152 g CaCO3 by the reaction below.

CaCO3(s) CaO(s) + CO2(g)


Limestone is dissolved by CO2 and water according to

the equation

CaCO3 + H2O + CO2 Ca(HCO3)2

What volume of CO2 measured at STP would dissolve

115g of CaCO3?

25.8 L CO2

Gas Stoichiometry Problem #4

Magnesium once used in flashbulbs, burns according to

the equation

2Mg + O2 2 MgO

What mass of Mg combines with 5.80 L of O2 measured

at STP?

12.6 g

Gas Stoichiometry Problem #5

Acetylene (C2H2) is produced from calcium carbide as

shown by the reaction

CaC2 (s) + 2H2O (l) Ca(OH)2 (s) + C2H2 (g)

What volume of acetylene measured at 25°C and 745

torr would be produced from 5.00 g of H2O?

3.47 L

Chem. Catalyst 7.5

At a given temperature and pressure, a 0.33 mol sample of

oxygen gas occupies a volume of 9.0 L. If this sample of gas

reacts with excess hydrogen to form water vapor at the

same conditions of temperature and pressure, what volume

will the water vapor occupy? Explain.

2 H2 (g) + O2 (g) 2 H2O (g)

Dalton’s Law of Partial Pressures

Neon gas (Ne) P = 740 mm Hg

Argon gas (Ar) P = 790 mm Hg

Helium gas (He) P = 740 mm Hg

The total pressure of a gas mixture is equal

to the sum of the partial pressures.

Imagine a cylinder with a fixed

volume is filled with three gases: Ar,

Ne and He. What is the total

pressure of the cylinder?

...total a b cP P P P

Dalton’s Law of Partial Pressures Problem #1

A balloon containing nitrogen and hydrogen gas has a

total pressure of 1.33 atmospheres. Calculate the partial

pressure of nitrogen gas if the partial pressure of

hydrogen gas is 0.45 atm.

Dalton’s Law of Partial Pressures Problem

A cylinder with a total pressure of

5.00 atmospheres contains 4 moles

of He gas and 5 moles of N2 gas.

Calculate the partial pressures of

each gas.

a a totalP P

Partial Pressure Mole Fraction Total Pressure

Dalton’s Law of Partial Pressures Problem 2

A study of the effects of certain gases on plant growth

requires a synthetic atmosphere composed of 1.5 mol

percent CO2, 18.0 mol percent O2, and 80.5 mol percent

Ar. Calculate the partial pressure of O2 in the mixture if

the total pressure of the atmosphere is 745 torr?

Kinetic Molecular Theory


www.mpcfaculty.net/mark_bishop/KMT.htm


Gases

Gases have mass and negligible volume.

Gas molecules move in straight lines and collide each

other with elastic collisions.

Speed of molecules is proportional to temperature of gas

sample.

Higher the temperature = faster the movement of gas

molecules

There are no attractive forces or repulsive forces

between gas molecules

Root Mean Square Velocity

Special kind of average of gas particles velocity

Root mean square velocity = urms

R =8.31 J/ mol x K

Gas Diffusion and Effusion

So far we have been able to consider all ideal gases to

behave in a similar fashion.

That is, we have been able to describe all gases as acting

the same way.

Now we will look at two properties of gases that depend

on the identity of the gas.

Diffusion

Effusion

Diffusion and Effusion of Gases

Diffusion Effusion

Rate at which two gases

mix

Gases move from high

concentration to low

concentration

spontaneously

Rate at which a gas

escapes through a pinhole

into a vacuum

Spontaneous process

Effusion and Diffusion of Gases

Rate of diffusion of gas a

Rate of diffusion of gas b

Molar masses of gas a and b

Graham’s Law

Gas Diffusion

NH3 diffuses faster than HCl because it has a smaller molecular mass. This

is why the two gases do not meet in the middle of the tube.

Chem. Catalyst 7 - De La Salle High SchoolChem. Catalyst 7.1 List a few ... Combined Gas Law 5....

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