1. 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
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2. What factors most strongly affect the weather?
CHEMISTRY & YOU
What factors most strongly affect the weather?
The atmosphere is a gas, and the factors that determine the behavior of gases—temperature and pressure—affect the weather in the atmosphere.
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3. Kinetic Theory and a Model for Gases
What are the three assumptions of the kinetic theory as it applies to gases?
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4. 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.
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5. 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.
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6. 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 the particles.
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7. 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.
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8. 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.
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9. 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.
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10. 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.
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11. Describe an elastic collision between gas molecules.
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12. 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.
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13. How does kinetic theory explain gas pressure?
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14. 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.
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15. Gas Pressure
Gas pressure is the result of billions of rapidly moving particles in a gas simultaneously colliding with an object.
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16. Gas Pressure
Gas pressure is the result of billions of rapidly moving particles in a gas simultaneously colliding with an object.
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.
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17. 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.
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18. A barometer is a device that is used to measure atmospheric pressure.
Gas Pressure
A barometer is a device that is used to measure atmospheric pressure.
Vacuum
Atmospheric pressure
760 mm Hg (barometric pressure)
253 mm Hg
Sea level
On top of Mount Everest
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.
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19. CHEMISTRY & YOU
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?
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20. CHEMISTRY & YOU
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?
When a storm approaches, the column of mercury goes down, indicating a decrease in atmospheric pressure.
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21. The SI unit of pressure is the pascal (Pa).
Gas Pressure
The SI unit of pressure is the pascal (Pa).
Normal atmospheric pressure is about 100,000 Pa, that is, 100 kilopascals (kPa).
Two older units of pressure are commonly used.
millimeters of mercury (mm Hg)
atmospheres (atm)
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22. 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 three units is
1 atm = 760 mm Hg = kPa.
Recall that standard temperature and pressure (STP) are defined as a temperature of 0°C and a pressure of kPa, or 1 atm.
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23. Converting Between Units of Pressure
Sample Problem 13.1
Converting Between Units of Pressure
A pressure gauge records a pressure of 450 kPa. Convert this measurement to
a. atmospheres
b. millimeters of mercury
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24. Analyze List the knowns and the unknowns.
Sample Problem 13.1
Analyze List the knowns and the unknowns. 1
The given pressure is converted into the desired unit by multiplying by the proper conversion factor.
KNOWNS
UNKNOWNS
pressure = ? atm
pressure = ? mm hg
pressure = 450 kPa
1 atm = kPa
1 atm = 760 mm Hg
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25. Calculate Solve for the unknowns.
Sample Problem 13.1
Calculate Solve for the unknowns. 2
Identify the appropriate conversion factor
1 atm
101.3 kPa
a. to convert kPa to atm.
101.3 kPa
760 mm Hg
b. to convert kPa to mm Hg.
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26. Calculate Solve for the unknowns.
Sample Problem 13.1
Calculate Solve for the unknowns. 2
Multiply the given pressure by the conversion factor.
b. 450 kPa × = 3400 mm Hg = 3.4 × 103 mm Hg
101.3 kPa
760 mm Hg
1 atm
a. 450 kPa × = 4.4 atm
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27. Evaluate Do the results make sense?
Sample Problem 13.1
Evaluate Do the results make sense? 3
Because the first conversion factor is much less than 1 and the second is much greater than 1, it makes sense that the values expressed in atm and mm Hg are respectively smaller and larger than the value expressed in kPa.
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28. What is the pressure in millimeters of mercury inside a vacuum?
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29. What is the pressure in millimeters of mercury inside a vacuum?
0 mm Hg
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30. Kinetic Energy and Temperature
What is the relationship between the temperature in kelvins and the average kinetic energy of particles?
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31. Kinetic Energy and Temperature
As a substance is heated, its particles absorb energy, some of which is stored within the particles.
This stored portion of the energy, or potential energy, does not raise the temperature of the substance.
The remaining absorbed energy does speed up the particles, that is, increases their kinetic energy.
This increase in kinetic energy results in an increase in temperature.
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32. Kinetic Energy and Temperature
Average Kinetic Energy
The particles in any collection of atoms or molecules at a given temperature have a wide range of kinetic energies.
Most have kinetic energies somewhere in the middle of this range.
We use average kinetic energy when discussing the kinetic energy of a collection of particles in a substance.
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33. Kinetic Energy and Temperature
Average Kinetic Energy
At any given temperature, the particles of all substances, regardless of physical state, have the same average kinetic energy.
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34. Interpret Graphs
The figure below shows the distribution of kinetic energies of water molecules at two different temperatures.
The green curve shows the distribution of kinetic energy in cold water.
The purple curve shows the distribution of kinetic energy in hot water.
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35. Interpret Graphs
The figure below shows the distribution of kinetic energies of water molecules at two different temperatures.
Most of the molecules have intermediate kinetic energies, close to the average value.
Notice that the molecules at the higher temperature have a wider range of kinetic energies.
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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.
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37. Kinetic Energy and Temperature
Average Kinetic Energy
Absolute zero (0 K, or –273.15oC) 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 K, which is 0.1 nanokelvin, has been achieved.
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38. 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.
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39. Kinetic Energy and Temperature
Average Kinetic Energy and Kelvin Temperature
The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of the substance.
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40. 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.
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41. 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.
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42. Key Concepts
Particles in a gas are considered to be small, hard spheres with an insignificant volume. The motion of the particles in a gas is rapid, constant, and random. All collisions between particles in a gas are perfectly elastic.
Gas pressure is the result of billions of rapidly moving particles in a gas simultaneously colliding with an object.
The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of the substance.
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43. kinetic energy: the energy an object has because of its motion
Glossary Terms
kinetic energy: the energy an object has because of its motion
kinetic theory: a theory explaining the states of matter, based on the concept that all matter consists of tiny particles that are in constant motion
gas pressure: results from the force exerted by a gas per unit surface area of an object; due to collisions of gas particles with the object
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44. vacuum: a space where no particles of matter exist
Glossary Terms
vacuum: a space where no particles of matter exist
atmospheric pressure: the pressure exerted by atoms and molecules in the atmosphere surrounding Earth, resulting from collisions of these particles with objects
barometer: an instrument used to measure atmospheric pressure
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45. Pascal (Pa): the SI unit of pressure
Glossary Terms
Pascal (Pa): the SI unit of pressure
standard atmosphere (atm): a unit of pressure; it is the pressure required to support 760 mm of mercury in a mercury barometer at 25°C
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46. END OF 13.1
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