Chapter 13: Gases. What Are Gases? Gases have mass Gases have mass.
Lesson 1 Unit 5 Gases and Atmospheric Chemistry. Particle Theory 1. All Matter is made up of...
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Transcript of Lesson 1 Unit 5 Gases and Atmospheric Chemistry. Particle Theory 1. All Matter is made up of...
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The Gas State and Kinetic Molecular Theory
Lesson 1Unit 5 Gases and Atmospheric Chemistry
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Particle Theory1. All Matter is made up of extremely tiny particles
2. Each Pure substance has its own kind of particles, different from the particles of other pure substances
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3. Particles are always moving. Particles at a higher temperature are generally moving faster, on average than particles at a lower temperature.
4. Particles attract each other
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There are three states of matter.Gas, Liquid, and Solid. All three of these
states are physical states of matter. There is also a forth, it is called a plasma which has charged particles that can conduct electricity and are influenced by magnetic fields. It is similar to a gas in its properties
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Phase Structure Movement of Particles
Shape of Sample
Density Compressibility
Solid - Particles closely packed - Particles in fixed positions
- Vibration
-Definite shape -Volume of its own
-Usually more dense than liquid or gas
-Cannot be compressed significantly
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Phase Structure Movement of Particles
Shape of Sample
Density Compressibility
Liquid
-Particles Closely packed - Particles not fixed in position
- Vibration - Rotation - Translation (slower)
- Takes shape of container - Volume of its own
- Usually less dense than solid
- Cannot be compressed significantly
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Phase Structure Movement of Particles
Shape of Sample
Density Compressibility
Gas - Particles widely spaced - Particles not fixed in position
- Vibration - Rotation, - Translation (fast)
- Occupies entire volume of container
- Much less dense than solid or liquid
- Can be easily compressed
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Two properties of matter that are particularly important to the study of fluids are density and compressibility.
Density – The mass per unit volume of a substance; it is a scalar quantity with SI units of kg/m3
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Laws vs Theories
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Laws are empirical generalizations which describes the results of several experiments.
It only describes results; it does not explain why the results have been explained.
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Theories are descriptions that explain results of experiments.
The kinetic molecular theory is used to help explain the following laws: Boyle, Charles, and Dalton.
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Kinetic Molecular Theory of GasesThere are 4 postulates
1. A gas consists of molecules in constant random motion
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Kinetic Molecular Theory of Gases2. Gas molecules influence each other only by
collision; they exert no other forces on each other.
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3. All collisions between gas molecules are perfectly elastic; all kinetic energy is conserved.
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4. The volume actually occupied by the molecules of a gas is negligibly small; the vast majority of the volume of the gas is empty space through which the gas molecules are moving.
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These 4 postulates correspond to a physical model of gas that we can think of like billiard balls on a billiards table for ideal gasses.
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Gasses at room temperatures and pressures at or below normal atmospheric pressures tend to behave as described by the postulates and the empirical gas laws in a quantitative way.
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Gas PressuresIn the KMT, pressure is the force exerted
against the wall of a container by the continual collision of molecules against it. Newton's second law of motion tells us that the
force exerted on a wall by a single gas molecule is equal to the mass of the molecule multiplied by the velocity of the molecule.
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The molecule rebounds elastically and no kinetic energy is lost in a collision. All the molecules in a gas do not have the same velocity. The average velocity is used to describe the
overall energy in a container of gas.
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The pressure volume product of the ideal gas equation is directly proportional to the average velocity of the gas molecules.
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It has been necessary to use the average velocity of the molecules of a gas because the actual velocities are distributed over a very wide range. This distribution, can be described by Maxwell's law of distribution of velocities. The root mean square velocity of a molecule can be calculated using the formula below.
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Where M is molecular mass divided by 1000, R is the molar gas constant (8.314 J/mol K) and Temperature in K. Molecules can be traveling easily around 2000km/h.
If gasses traveled this speed in a room we would smell things instantly, we don’t because the molecules only travel a short distance before colliding with other molecules and changing direction.
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Read 416 – 422 # Practice 1- 4, section 9.1 # 1-5.