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. 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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3. 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 (1/2mv2).
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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.
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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5. 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.
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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.
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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7. 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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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 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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9. 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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10. Kinetic energy and gases
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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. 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
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14. How does kinetic theory explain gas pressure?
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15. 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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16. 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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17. 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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18. 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 (fewer collisions) as the elevation increases.
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19. 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.
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?
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21. 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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22. 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).
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
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23. The Mole-Volume Relationship
Avogadro’s Hypothesis
Recall Avogadro’s hypothesis states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.
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24. The Mole-Volume Relationship
Avogadro’s Hypothesis
The volume of a gas varies with a change in temperature or a change in pressure.
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 kPa, or 1 atmosphere (atm).
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25. The Mole-Volume Relationship
Avogadro’s Hypothesis
Recall 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.
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26. Gas Pressure
One standard atmosphere (atm) is the pressure required to support 760 mm of mercury in a mercury barometer at 25°C.
1 atm = 760 mm Hg = 760 Torr = kPa.
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27. What is the pressure in millimeters of mercury inside a vacuum?
Zero!
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28. 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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29. 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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30. 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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31. Celsius – Kelvin temperature conversions 273K = 0 Cº or 285 K =
Celsius – Kelvin temperature conversions 273K = 0 Cº or 285 K = ? ºC 12 K = 285 ºC K = ? ºC 43 ? K = 222 ºC 495
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32. 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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33. 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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34. END OF 13.1
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