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# Learning about the special behavior of gases

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Learning about the special behavior of gases
The Gas Laws Learning about the special behavior of gases

The States of Matter A) What are the 3 states of matter that chemists work with? Solids, liquids, and gases B) We will explain the behavior of gases using the Kinetic Molecular Theory

The Kinetic Molecular Theory
1. What is Kinetic Energy- the energy of motion K.E. = ½(mass)(velocity)2 Molecules are in motion! Solids - a bit Liquids - a bit more Gases - a whole bunch!

The Kinetic Molecular Theory
2. Define the Kinetic Molecular Theory as it pertains to gases: atoms and molecules of gases are in constant, random motion. We will focus on gases only and use the kinetic theory to explain their behavior.

3 Basic Assumptions of the Kinetic Theory
a. A gas is composed of particles, usually molecules or atoms. The atoms occupy a negligible volume compared to their container! No attractive or repulsive forces between molecules.

Second Assumption b. The particles in a gas move rapidly in constant random motion. The molecules travel in straight lines and move independently of each other. They change direction only when they rebound from collisions with one another or with other objects.

Third Assumption c. All collisions are perfectly elastic
‘perfectly elastic’ means that energy is transferred from one particle to another during collisions, but the total energy remains the same.

4. Question to Ponder: If we opened a perfume bottle in Washington D.C., the gas molecules should reach Mexico City in about 90 minutes… Why don’t they ever make it? They collide with too many other things and never make the trip.

5. Define random walk - The aimless path molecules take as they diffuse from areas of higher concentration to areas of lower concentration. Review the definition of diffuse with your neighbor.

Gas Pressure pg. 268 A. Define Gas Pressure - the result of simultaneous collisions of billions and billions of gas particles on an object. B. Define Vacuum - absence of particles, no pressure empty space caused by removing gas molecules

C. Define Atmospheric Pressure - results from the collisions of air molecules with objects
D. What is a Barometer - a device used to measure air pressure

Units of Pressure Pressure can be measured in 3 different units:
 Pascal - the SI unit of pressure (kiloPascals) 101.3 kPa is Standard Pressure  mmHg - (millimeters of mercury) - one mm of Hg is the pressure needed to support a column of mercury 1 mm high. 760 mm Hg is standard pressure  atm- atmosphere - the average atmospheric pressure at sea level. 1 atm is standard pressure

Standard Conditions pg. 2
F. Standard Pressure and Temperature defined: Standard Pressure: 1 ATM = 760 mmHg = kPa Standard Temperature 0o Celsius or 273 Kelvin To find Kelvin…. Kelvin = Celsius

Practice converting Example 1: A gas is at a pressure of 1.5 atm. Covert this pressure to kPa mm Hg

( ) Practice converting
Example 1: A gas is at a pressure of 1.5 atm. Covert this pressure to kPa 1.5 atm 1 mm Hg ( )

( ) ( ) Practice converting
Example 1: A gas is at a pressure of 1.5 atm. Covert this pressure to kPa 1.5 atm kPa = kPa atm mm Hg ( ) ( )

( ) ( ) ( ) ( ) Practice converting
Example 1: A gas is at a pressure of 1.5 atm. Covert this pressure to kPa 1.5 atm kPa = kPa atm mm Hg 1.5 atm mmHg = 1,140 mmHg atm ( ) ( ) ( ) ( )

Practice Converting Example 2: What pressure, in kilopascals and in atmospheres, does a gas exert at 385 mm Hg? Please work with you neighbor

( )( ) ( ) ( ) Practice Converting
Example 2: What pressure, in kilopascals and in atmospheres, does a gas exert at 385 mm Hg? 385 mmHg kPa = kPa mmHg 385 mmHg atm = atm ( )( ) ( ) ( )

Practice Converting Example 3: The Pressure at the top of Mount Everest is 33.7 kPa. Is that pressure greater or less than 0.25 atm?

( ) ( ) Practice Converting
Example 3: The Pressure at the top of Mount Everest is 33.7 kPa. Is that pressure greater or less than 0.25 atm? 33.7 kPa atm = atm kPa A: Yes, 0.33 atm is greater than 0.25 atm ( ) ( )

Kinetic Energy and Kelvin Temperature pg. 269-271
A. Why do gas molecules contain Kinetic Energy? They are in constant motion B. What happens to the amount of kinetic energy a object contains as it is heated? The Kinetic Energy increases as the Kelvin temperature increases. (Directly related)

Important Relationship
C. The average kinetic energy of the particles of a substance is proportional to the temperature of the substance. D. Particles of all substances at the same temperature have the same average kinetic energy.

Important Relationship
E. Theoretically, there is no upper limit to which a substance’s temperature can be raised. By contrast, there is a lower limit…

F. What is the term used to describe the temperature at which the motion of particles ceases ~ no more Kinetic Energy? Absolute Zero

G. The values of Absolute Zero…
0 Kelvin or -273 Celsius H. THE KELVIN SCALE IS USED TO DIRECTLY MEASURE THE KINETIC ENERGY OF AN OBJECT, NOT THE CELSIUS SCALE!

Ch. 12 The Behavior of Gases (Notepack pg. 3)
How does adding molecules into a container, keeping volume and temperature constant, effect the pressure inside the container? More molecules results in an increased pressure BECAUSE they will strike the side of the container more often = higher pressure

In contrast… How does removing particles, keeping volume and temp constant, affect the pressure? Lowers it because fewer particles = fewer collisions against the side of the container

The effect of Changing the Size of the Container:
What happens to the pressure inside of a container when we reduce the volume, keeping temp constant? Increases because shorter distance traveled before a collision against the side What happens if we increase the volume? Lower pressure because greater distance traveled means fewer collisions

The Effect of Heating or Cooling a Gas
How does raising the temperature affect pressure if volume is constant? INCREASE = increased kinetic energy = molecules move faster and strike the side more often. How does lowering the temperature affect pressure if volume is constant? DECREASE - lowered KE = move slower =fewer collisions

HOMEWORK Please spend some time reading over these notes, mentally engaging in the content.

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