General organic and biological chemistry structures off life 5th CH8 properties of gases GOB structures 5th ed

When volume increases, the pressure decreases, provided the temperature and moles of the gas remains constant.. What is the new volume of an 8.0 L sample of Freon gas initially at 550 mm

Karen C Timberlake

Lecture Presentation

Chapter 8 Gases

Chapter 8 Gases

Respiratory therapists assess

and treat a range of patients

They perform a variety of

diagnostic tests, including

measuring

• breathing capacity

• concentrations of oxygen

and carbon dioxide in a

patient’s blood, as well as

blood pH

Chapter 8 Readiness

Key Math Skills

• Solving Equations (1.4D)

Core Chemistry Skills

Equalities (2.5)

• oxides of the nonmetals on the

upper-right corner of the

periodic table: CO,

CO2, NO, NO2, SO2,

and SO3

He Ne Ar Kr Xe Rn

F O

N C

H

Kinetic Molecular Theory

A gas consists of small particles that

1 move randomly with high

velocities

2 have very small attractive (or

repulsive) forces between

molecules

3 occupy a much larger volume than

the volume of the molecules alone

4 are in constant motion, moving

rapidly in straight lines

5 have a Kelvin temperature

proportionate to the average kinetic

energy of the molecules

Gas particles which move in straight lines within a container, exert pressure when they

collide with the walls of the container.

Properties That Describe a Gas

Gases are described in terms of four properties: pressure (P), volume (V), temperature (T), and amount (n).

The volume of a gas

• is the same as the volume

of the container it occupies

• is usually measured in

liters or milliliters

• increases with an increase

in temperature at a

constant pressure Gas particles which

move in straight lines within a container, exert pressure when they

collide with the walls of the container.

The temperature of a gas relates to the average

kinetic energy of the molecules and is measured in

the Kelvin (K) temperature scale.

When the temperature of a gas is

• decreased, the molecules have fewer collisions.

• increased, the molecules have more collisions.

Pressure is a measure of the gas

particle collisions with sides of a

container and is measured in units of

• millimeters of mercury, mmHg

or torr

• atmospheres, atm

• pascals, Pa, or kilopascals, kPa

• pounds per square inch, psi

Gas particles in the air exert

pressure on us called

atmospheric pressure.

Barometers Measure Pressure

A barometer

• measures the pressure exerted

by the gases in the atmosphere

• indicates atmospheric pressure

as the height in mm of the

mercury column

760 mmHg = 1 atm = 760 Torr

The barometer was invented by

Units of Pressure

Atmospheric Pressure

Atmospheric pressure

• is the pressure exerted by a

column of air from the top of

the atmosphere to the

Altitude and Atmospheric Pressure

Atmospheric pressure changes with variations in weather and altitude

• On a hot, sunny day, the mercury column rises,

indicating a higher atmospheric pressure.

• On a rainy day, the atmosphere exerts less pressure, which causes the mercury column to fall.

1 What is 475 mmHg expressed in atm?

The answer is B, 0.625 atm.

2 The pressure in a tire is 2.00 atm What is this

pressure in mmHg?

The answer is B, 1520 mmHg.

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Study Check

1 The downward pressure on the Hg in a barometer

is _ the pressure of the atmosphere.

A greater than B less than C the same as

2 A water barometer is 13.6 times taller than an Hg

1 The downward pressure on the Hg in a barometer

is _ the pressure of the atmosphere.

The answer is C, the same as.

2 A water barometer is 13.6 times taller than an Hg

The answer is A, H2O is less dense than

mercury.

8.2 Pressure and Volume, (Boyle’s Law)

The inverse relationship between

the pressure and volume of a gas is

known as Boyle’s law

Changes occur in opposite

directions When volume increases,

the pressure decreases, provided

the temperature and moles of the

gas remains constant

Learning Goal Use the pressure–volume relationship

(Boyle’s law) to determine the final pressure or volume

when the temperature and amount of gas are constant

The anesthetic N2O gas,

is used for pain relief.

Boyle’s Law

Boyle’s law states that

• the pressure of a gas is

inversely related to its

volume when T is constant.

• the product P  V is

constant when temperature

and amount of a gas is

held constant

• if volume decreases, the

pressure increases

P1V1 = P2V2

Boyle’s Law: PV = Constant

Pressure × volume is a constant, provided the

temperature and amount of the gas remains

Chemistry Link to Health:

Boyle’s Law and Breathing

During an inhalation,

• the lungs expand.

• the pressure in the lungs

decreases.

• air flows toward the lower

pressure in the lungs.

Chemistry Link to Health:

Boyle’s Law and Breathing

During an exhalation,

• lung volume decreases.

• pressure within the lungs

increases.

• air flows from the higher

pressure in the lungs to

the outside.

Guide to Using Gas Laws

Calculations Using Boyle’s Law

Freon-12, CCl2F2, was used in refrigeration systems What is the new volume of an 8.0 L sample of Freon gas initially at 550 mmHg after its pressure is changed to 2200 mmHg at constant temperature and moles?

STEP 1 Organize the data in a table of initial and final conditions.

Temperature and moles remain constant

ANALYZE Conditions 1 Conditions 2 Know Predict

Calculations Using Boyle’s Law

STEP 2 Rearrange the gas law equation to solve for the unknown quantity.

P1V1 = P2V2 Boyle’s law

To solve for V2 , divide both sides by P2

STEP 3 Substitute values into the gas law equation and

calculate.

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Study Check

For a cylinder containing helium gas, indicate if cylinder A

or cylinder B represents the new volume for the following

changes (n and T are constant).

1 pressure decreases

2 pressure increases

For a cylinder containing helium gas, indicate if cylinder A

or cylinder B represents the new volume for the following

changes (n and T are constant).

1 pressure decreases cylinder B

2 pressure increases cylinder A

Study Check

If a sample of helium gas has a volume of 120 mL and a

pressure of 850 mmHg, what is the new volume if the pressure

is changed to 425 mmHg at a constant T and n?

A 60 mL

B 120 mL

C 240 mL

If a sample of helium gas has a volume of 120 mL and a

pressure of 850 mmHg, what is the new volume if the pressure

is changed to 425 mmHg at a constant T and n?

STEP 1 Organize the data in a table of initial and final

conditions.

Temperature and moles remain constant

If a sample of helium gas has a volume of 120 mL and a

pressure of 850 mmHg, what is the new volume if the pressure

is changed to 425 mmHg at a constant T and n?

STEP 2 Rearrange the gas law equation to solve for the unknown quantity

STEP 3 Substitute values into the gas law equation

and calculate

×

×

Study Check

A sample of helium gas in a balloon has a volume of 6.4 L at a

pressure of 0.70 atm At 1.40 atm (T and n are constant), is

the new volume represented by A, B, or C?

A sample of helium gas in a balloon has a volume of 6.4 L at a

pressure of 0.70 atm At 1.40 atm (T and n are constant), is

the new volume represented by A, B, or C?

At a higher pressure (T and n constant), the new volume is

represented by the smaller balloon A.

8.3 Temperature and Volume

(Charles’s Law)

If we increase the temperature of a

gas sample, kinetic molecular

theory states that the motion

(kinetic energy) of the gas particles

will also increase

If the amount and pressure of the

gas is held constant, the volume of

the container will increase

Learning Goal Use the temperature–volume relationship

(Charles’s law) to determine the final temperature or volume

when the pressure and amount of gas are constant

Charles’s Law

In Charles’s law,

• the Kelvin temperature (K)

of a gas is directly related

to its volume

• pressure and moles of gas

are constant

• when the temperature of a

sample of gas increases,

its volume increases at

constant pressure

Charles’s Law: V and T

(P and n are constant)

Study Check

Calculations Using Charles’s Law

A balloon has a volume of 785 mL at 21 °C If the temperature drops to 0 °C, what is the new volume of the balloon at

constant pressure and moles?

STEP 1 Organize the data in a table of initial and final

conditions.

Calculations Using Charles’s Law

STEP 2 Rearrange to solve for unknown quantity: V2

Study Check

A sample of oxygen gas has a volume of 420 mL at a

temperature of 18 °C At what temperature (in °C) will

the volume of the oxygen be 640 mL (P and n are

constant)?

A 443 °C

B 170 °C

C −82 °C

A sample of oxygen gas has a volume of 420 mL at a

temperature of 18 °C At what temperature (in °C) will the

volume of the oxygen be 640 mL (P and n are constant)?

STEP 1 Organize the data into a table of initial and final conditions.

Pressure and moles remain constant

ANALYZE Conditions 1 Conditions 2 Know Predict

A sample of oxygen gas has a volume of 420 mL at a

temperature of 18 °C At what temperature (in °C) will the

volume of the oxygen be 640 mL (P and n are constant)?

STEP 2 Rearrange to solve for unknown quantity: T2

-Study Check

Use the gas laws to complete each sentence with increases

or decreases

A Pressure _ when V decreases at constant

temperature and moles

B When T decreases, V _ at constant pressure and

moles

C Pressure _ when V changes from 12 L to 24 L at

constant temperature and moles

D Volume _when T changes from 15 °C to 45 °C at

constant pressure and moles

Use the gas laws to complete each sentence with increases

or decreases

A Pressure increases when V decreases at constant

temperature and moles

B When T decreases, V decreases at constant pressure

and moles

C Pressure decreases when V changes from 12 L to 24 L at

constant temperature and moles

D Volume increases when T changes from 15 °C to 45 °C at

constant pressure and moles

8.4 Temperature and Pressure

(Gay-Lussac’s Law)

Gay-Lussac’s law:

When the Kelvin temperature

of a gas doubles at constant

volume and amount of gas,

the pressure also doubles.

Gay-Lussac’s Law

In Gay-Lussac’s law,

• the pressure exerted by a

gas is directly related to

the Kelvin temperature of

the gas.

• volume and amount of gas

are constant.

Study Check

Solution

Calculations Using Gay-Lussac’s Law

A gas has a pressure at 2.0 atm at 18 °C What is the new

pressure when the temperature is 62 °C (constant volume

and moles)?

STEP 1 Organize the data in a table of initial and final

conditions.

Calculations Using Gay-Lussac’s Law

STEP 2 Rearrange to solve for unknown quantity P2

Solve Gay-Lussac’s law for P2:

STEP 3 Substitute the values into the gas law equation

and calculate

×

×

Study Check

A gas has a pressure of 645 Torr at 128 °C

What is the temperature in Celsius if the

pressure increases to 824 Torr (V and n

remain constant)?

A gas has a pressure of 645 Torr at 128 °C What is the

temperature in Celsius if the pressure increases to 824 Torr

(V and n remain constant)?

STEP 1 Organize the data in a table of initial and final

conditions

Volume and moles remain constant

A gas has a pressure of 645 Torr at 128 °C What is the

temperature in Celsius if the pressure increases to 824 Torr

(V and n remain constant)?

STEP 2 Rearrange to solve for unknown quantity T2

Solve Gay-Lussac’s law for T2:

STEP 3 Substitute the values into the gas law equation

and calculate

×

-Vapor Pressure and Boiling Point

When liquid molecules with sufficient kinetic energy break away from the surface of a liquid, they become a vapor

• In an open container, all the liquid will eventually evaporate

• In a closed container, the vapor accumulates and creates

pressure called vapor pressure

A liquid

• exerts its own vapor pressure at a given temperature

• boils when its vapor pressure becomes equal to the external pressure

Altitude and Boiling Point

At high altitudes,

• atmospheric pressure is

lower than 1 atm, 760 Torr

• the boiling point of water is

lower than 100 °C.

In a closed container, such as

a pressure cooker,

• a pressure greater than

1 atm, 760 Torr, can be

obtained

• water boils at a higher

temperature than 100 °C.

Vapor Pressure and Boiling Point

Study Check

Explain why water boils at a lower

temperature in the mountains than at

sea level.

Explain why water boils at a lower

temperature in the mountains than at

sea level.

Atmospheric pressure in the mountains is

less than at sea level The vapor pressure of

the water reaches the atmospheric pressure

at a lower temperature.

8.5 The Combined Gas Law

Under water, the pressure on a

diver is greater than the

Learning Goal Use the combined gas law to calculate the

final pressure, volume, or temperature of a gas when

changes in two of these properties are given and the

amount of gas is constant

The Combined Gas Law

The combined gas law uses the pressure–volume–

temperature relationships from Boyle’s law, Charles’s law, and

Gay-Lussac’s law where n is constant.

Calculations Using Combined Gas Law

A gas has a volume of 675 mL at 35 °C and 646 mmHg

pressure What is the volume (mL) of the gas at −95 °C and a

pressure of 802 mmHg (n is constant)?

STEP 1 Organize the data into a table of initial and final

conditions.

Moles of gas remain the same

ANALYZE Conditions 1 Conditions 2 THE P1 = 646 mmHg P2 = 802 mmHg

PROBLEM V1 = 675 mL V2 = ?

T1 = 35 C + 273 T2 = −95 C + 273 = 308 K = 178 K

ANALYZE Conditions 1 Conditions 2 THE P1 = 646 mmHg P2 = 802 mmHg

PROBLEM V1 = 675 mL V2 = ?

T1 = 35 C + 273 T2 = −95 C + 273 = 308 K = 178 K

Calculations Using Combined Gas Law

STEP 2 Rearrange to solve for unknown quantity V2

STEP 3 Substitute the values into the gas law equation

and calculate

Study Check

A sample of helium gas has a volume of 0.180 L, a

pressure of 0.800 atm, and a temperature of 29 °C

At what temperature (°C) will the helium have a

volume of 90.0 mL and a pressure of 3.20 atm

(n remains constant)?

A sample of helium gas has a volume of 0.180 L, a pressure of

0.800 atm, and a temperature of 29 °C At what temperature

(°C) will the helium have a volume of 90.0 mL and a pressure

of 3.20 atm (n remains constant)?

STEP 1 Organize the data into a table of initial and final

conditions.

ANALYZE Conditions 1 Conditions 2

THE P1 = 0.800 atm P2 = 3.20 atm

A sample of helium gas has a volume of 0.180 L, a pressure of

0.800 atm, and a temperature of 29 °C At what temperature

(°C) will the helium have a volume of 90.0 mL and a pressure

of 3.20 atm (n remains constant)?

STEP 2 Rearrange to solve for unknown quantity T2

A sample of helium gas has a volume of 0.180 L, a pressure of

0.800 atm, and a temperature of 29 °C At what temperature

(°C) will the helium have a volume of 90.0 mL and a pressure

of 3.20 atm (n remains constant)?

STEP 3 Substitute the values into the gas law equation

and calculate.

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