1 of 36

Chapter 13

States of Matter

13.1 The Nature of Gases

13.2 The Nature of Liquids

13.3 The Nature of Solids

13.4 Changes of State

13.1 The Nature of Gases >

1

2 of 36

I CAN ….

Describe the kinetic theory of gases

Describe gas pressure and how it is measured

Ex[plain the meaning of standard temperature and pressure or STP

Define molar volume of a gas and how it relates to STP

Convert between Kelvin (K) and Celsius (C⁰) temperature scales

13.1 The Nature of Gases >

2

3 of 36

Daily Question

What factors most strongly affect the weather?

CHEMISTRY & YOU

The atmosphere is a gas, and the factors that determine the behavior of gases—temperature and pressure—affect the weather in the atmosphere.

13.1 The Nature of Gases >

3

4 of 36

Kinetic Theory and a Model for Gases

What are the three assumptions of the kinetic theory as it applies to gases?

13.1 The Nature of Gases >

4

5 of 36

Kinetic Theory and a Model for Gases

The word kinetic refers to motion.

The energy an object has because of its motion is called kinetic energy.

13.1 The Nature of Gases >

5

6 of 36

Kinetic Theory and a Model for Gases

The word kinetic refers to motion.

The energy an object has because of its motion is called kinetic energy.
According to the kinetic theory, all matter consists of tiny particles that are in constant motion.
The particles in a gas are usually molecules or atoms.

13.1 The Nature of Gases >

6

7 of 36

Kinetic Theory and a Model for Gases

The kinetic theory as it applies to gases includes the following fundamental assumptions about gases.

The particles in a gas are considered to be small, hard spheres with an insignificant volume.

Within a gas, the particles are relatively far apart compared with the distance between particles in a liquid or solid.
Between the particles, there is empty space.
No attractive or repulsive forces exist between gas particles.

13.1 The Nature of Gases >

7

8 of 36

Kinetic Theory and a Model for Gases

The kinetic theory as it applies to gases includes the following fundamental assumptions about gases.

Bromine molecule

The motion of particles in a gas is rapid, constant, and random.

Gases fill their containers regardless of the shape and volume of the containers.
An uncontained gas can spread out into space without limit.

13.1 The Nature of Gases >

8

9 of 36

Kinetic Theory and a Model for Gases

The kinetic theory as it applies to gases includes the following fundamental assumptions about gases.

The motion of particles in a gas is rapid, constant, and random.

The rapid, constant motion of particles in a gas causes them to collide with one another and with the walls of their container.

13.1 The Nature of Gases >

9

10 of 36

Kinetic Theory and a Model for Gases

The kinetic theory as it applies to gases includes the following fundamental assumptions about gases.

The motion of particles in a gas is rapid, constant, and random.

The particles travel in straight-

line paths until they collide with another particle.

The particles change direction only when they rebound from collisions.

13.1 The Nature of Gases >

10

11 of 36

Kinetic Theory and a Model for Gases

The kinetic theory as it applies to gases includes the following fundamental assumptions about gases.

All collisions between particles in a gas are perfectly elastic.

During an elastic collision, kinetic energy is transferred without loss from one particle to another.
The total kinetic energy remains constant.

13.1 The Nature of Gases >

11

12 of 36

Describe an elastic collision between gas molecules.

13.1 The Nature of Gases >

12

13 of 36

Describe an elastic collision between gas molecules.

An elastic collision is one in which kinetic energy is transferred from one particle to another with no overall loss of kinetic energy.

13.1 The Nature of Gases >

13

14 of 36

Kinetic Theory Review

What are the 3 parts of the kinetic theory?

Tiny particles insignificant volume

Rapid, random, constant motion

Collisions perfectly elastic- no loss of KE

13.1 The Nature of Gases >

14

15 of 36

Gas Pressure

How does kinetic theory explain gas pressure?

13.1 The Nature of Gases >

15

16 of 36

Gas Pressure

Gas pressure results from the force exerted by a gas per unit surface area of an object.

Moving bodies exert a force when they collide with other bodies.

13.1 The Nature of Gases >

16

17 of 36

Gas Pressure

Gas pressure is the result of billions of rapidly moving particles in a gas simultaneously colliding with an object.

13.1 The Nature of Gases >

17

18 of 36

Gas Pressure

If no particles are present, no collisions can occur. Consequently, there is no pressure.
An empty space with no particles and no pressure is called a vacuum.

Gas pressure is the result of billions of rapidly moving particles in a gas simultaneously colliding with an object.

13.1 The Nature of Gases >

18

19 of 36

Gas Pressure

Air exerts pressure on Earth because gravity holds the particles in air within Earth’s atmosphere.

The collisions of atoms and molecules in air with objects results in atmospheric pressure.
Atmospheric pressure decreases as you climb a mountain because the density of Earth’s atmosphere decreases as the elevation increases.
Fewer air particles means fewer collisions resulting in lower air pressure

13.1 The Nature of Gases >

19

20 of 36

Gas Pressure

A barometer is a device that is used to measure atmospheric pressure.

At sea level, air exerts enough pressure to support a 760-mm column of mercury.
On top of Mount Everest, at 9000 m, the air exerts only enough pressure to support a 253-mm column of mercury.
WHY?

Vacuum

Atmospheric pressure

760 mm Hg (barometric pressure)

253 mm Hg

Sea level

On top of Mount Everest

13.1 The Nature of Gases >

20

21 of 36

When weather forecasters state that a low-pressure system is moving into your region, it usually means that a storm is coming. What do you think happens to the column of mercury in a barometer as a storm approaches? Why?

CHEMISTRY & YOU

13.1 The Nature of Gases >

21

22 of 36

When weather forecasters state that a low-pressure system is moving into your region, it usually means that a storm is coming. What do you think happens to the column of mercury in a barometer as a storm approaches? Why?

CHEMISTRY & YOU

When a storm approaches, the column of mercury goes down, indicating a decrease in atmospheric pressure.

13.1 The Nature of Gases >

22

23 of 36

Gas Pressure

The SI unit of pressure is the pascal (Pa).

Normal atmospheric pressure is about 100,000 Pa, that is, 100 kilopascals (kPa).
Other units of pressure are commonly used.

millimeters of mercury (mm Hg)
atmospheres (atm)
torr (Torr) is defined as exactly 1/760 of a standard atomosphere

13.1 The Nature of Gases >

23

24 of 36

The Mole-Volume Relationship

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

.

Avogadro’s Hypothesis

13.1 The Nature of Gases >

24

25 of 36

13.1 The Nature of Gases >

25

26 of 36

The Mole-Volume Relationship

The volume of a gas varies with a change in temperature or a change in pressure.

.

Avogadro’s Hypothesis

Due to these variations with temperature and pressure, the volume of a gas is usually measured at standard temperature and pressure.
Standard temperature and pressure (STP) means a temperature of 0°C and a pressure of 101.3 kPa, or 1 atmosphere (atm).

13.1 The Nature of Gases >

26

27 of 36

The Mole-Volume Relationship

At STP, 1 mol, or 6.02 × 10²³ representative particles, of any gas occupies a volume of 22.4 L.

The quantity, 22.4 L, is called the molar volume of a gas.

.

Avogadro’s Hypothesis

13.1 The Nature of Gases >

27

28 of 36

Gas Pressure

One standard atmosphere (atm) is the pressure required to support 760 mm of mercury in a mercury barometer at 25°C.

The numerical relationship among the pressure units is

1 atm = 760 mm Hg = 760 Torr = 101.3 kPa.

Recall that standard temperature and pressure (STP) are defined as a temperature of 0°C and a pressure of 101.3 kPa, or 1 atm.

13.1 The Nature of Gases >

28

29 of 36

What is the pressure in millimeters of mercury inside a vacuum?

13.1 The Nature of Gases >

29

30 of 36

Kinetic Energy and Temperature

Average Kinetic Energy

The average kinetic energy of the particles in a substance is directly related to the substance’s temperature.

An increase in the average kinetic energy of the particles causes the temperature of a substance to rise.
As a substance cools, the particles tend to move more slowly, and their average kinetic energy decreases.

13.1 The Nature of Gases >

30

31 of 36

Kinetic Energy and Temperature

Average Kinetic Energy

Absolute zero (0 K, or –273.15^oC) is the temperature at which the motion of particles theoretically ceases.

No temperature can be lower than absolute zero.
Absolute zero has never been produced in the laboratory.

A near-zero temperature of about 0.000 000 000 1 K, which is 0.1 nanokelvin, has been achieved.

13.1 The Nature of Gases >

31

32 of 36

Kinetic Energy and Temperature

Average Kinetic Energy

The coldest temperatures recorded outside the laboratory are from space.

Astronomers used a radio telescope to measure the temperature of the boomerang nebula.
At about 1 K, it is the coldest known region of space.

13.1 The Nature of Gases >

32

33 of 36

Celsius – Kelvin temperature conversions 273K = 0 C⁰or

285 K = ? C⁰

¹²

K = 285 C⁰

⁵¹⁸

322 K = ? C⁰

⁴³

? K = 222 C⁰

⁴⁹⁵

13.1 The Nature of Gases >

33

34 of 36

What is the result of increasing the temperature of a gas sample?

A. A decrease in the average kinetic energy of the sample

B. No effect on the sample

C. An increase in the average kinetic energy of the sample

D. The particles slow down.

13.1 The Nature of Gases >

34

35 of 36

What is the result of increasing the temperature of a gas sample?

A. A decrease in the average kinetic energy of the sample

B. No effect on the sample

C. An increase in the average kinetic energy of the sample

D. The particles slow down.

13.1 The Nature of Gases >

35

36 of 36

END OF 13.1

13.1 The Nature of Gases >

36