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

Lecture Presentation

Chapter 8

Gases

Karen C. Timberlake

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


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.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Chapter 8 Readiness

Key Math Skills

•

Solving Equations (1.4D)

Core Chemistry Skills

•
•
•
•
•

Using Significant Figures in Calculations (2.3)
Writing Conversion Factors from Conversion Equalities (2.5)
Using Conversion Factors (2.6)
Using Molar Mass as a Conversion Factor (7.5)
Using Mole–Mole Factors (7.6)

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

8.1 Properties of Gases

Generally molecules with fewer than five atoms from the first two periods in the periodic table are gases at
room temperature. In addition, the following are also gases:

He

•

H2, N2, O2, F2, and Cl2

•

oxides of the nonmetals on the upper-right corner of
the periodic table: CO,
NO2, SO2, and SO3

•

H
CO 2, NO,

C N

O

F

S

Cl Ar

Ne
Kr
Xe

noble gases

Rn
Learning Goal Describe the kinetic molecular theory of gases and the units of measurement used for
gases.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Kinetic Molecular Theory

A gas consists of small particles that

1.
2.

move randomly with high velocities.
have very small attractive (or
repulsive) forces between molecules.

3.

occupy a much larger volume than the volume of the
molecules alone.

4.
5.

are in constant motion, moving rapidly in straight lines.
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.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Properties That Describe a Gas

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

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Volume

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.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Temperature

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.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Pressure

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.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


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 Evangelista Torricelli, at exactly 1
atm the barometer tube measures exactly 760 mm high.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Units of Pressure

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Atmospheric Pressure

Atmospheric pressure

•

is the pressure exerted by a column of air from the
top of the atmosphere to the surface of Earth.

•

decreases as altitude increases.

•

about 1 atm at sea level.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


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.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Study Check

1.

What is 475 mmHg expressed in atm?

A.
B.
C.

475 atm
0.625 atm
5
3.61 × 10 atm

2. The pressure in a tire is 2.00 atm. What is this
pressure in mmHg?

D.
E.
F.

2.00 mmHg
1520 mmHg
22 300 mmHg

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Solution

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.

×
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Study Check

1.

The downward pressure on the Hg in a barometer is _____ the pressure of the
atmosphere.
A. greater than

2.

B. less than

C. the same as

A water barometer is 13.6 times taller than an Hg barometer (dHg = 13.6 g/mL) because
A. H2O is less dense than mercury.
B. H2O is heavier than mercury.
C. air is more dense than H2O.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Solution

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 barometer (dHg = 13.6 g/mL) because
The answer is A, H2O is less dense than mercury.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


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.

The anesthetic N2O gas, is used for pain
relief.

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.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


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

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


Boyle’s Law: PV = Constant

Pressure × volume is a constant, provided the temperature and amount of the gas
remains
the same.
P1V1 = 8.0 atm × 2.0 L = 16 atm L
P2V2 = 4.0 atm × 4.0 L = 16 atm L
P3V3 = 2.0 atm × 8.0 L = 16 atm L

Boyle’s law can be stated as
P1V1 = P2V2 (T is constant.)

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


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.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


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.

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.

Guide to Using Gas Laws

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

© 2016 Pearson Education, Inc.


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

ANALYZE
THE

Conditions 1
P1 = 550 mmHg

Conditions 2

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake

Predict

P2 = 2200 mmHg P increases

Temperature
remain
PROBLEM and
V = moles
8.0 L
V constant.
= ?
1

Know

conditions.

2

V decreases

© 2016 Pearson Education, Inc.