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### Chapter 3

States of Matter

Kinetic Theory

- Kinetic means motion
- Three main parts of the theory
- All matter is made of tiny particles
- These particles are in constant motion and the higher the temperature, the faster they move
- At the same temperature, heavier particles move slower.

Kinetic Theory

lare evidence of this.

- Kinetic theory says that molecules are in constant motion.
- Perfume molecules moving across the room

The Kinetic Theory of GasesMakes three assumptions about gases

- A Gas is composed of particles
- usually molecules or atoms
- Considered to be hard spheres far enough apart that we can ignore their volume.
- Between the molecules is empty space.

The particles are in constant random motion.

- Move in straight lines until they bounce off each other or the walls.
- All collisions are perfectly elastic

The Average speed of an oxygen molecule is 1656 km/hr at 20ºC

- The molecules don’t travel very far without hitting each other so they move in random directions.

Kinetic Energy and Temperature

- Temperature is a measure of the Average kinetic energy of the molecules of a substance.
- Higher temperature faster molecules.
- At absolute zero (0 K) all molecular motion would stop.

States of Matter

- Solid- matter that has a definite shape and volume
- Liquid- matter that flows and has a fixed volume
- Gas- matter that takes up both the shape and volume of a container
- Vapor- a substance that is currently a gas but normally is a liquid or solid at room temperature.
- Plasma- matter consisting of a gaseous mixture of electrons and positive ions. Not found on Earth

States of Matter

- Solid
- Particles are tightly packed
- Stuck to each other in a pattern
- Vibrate in place
- Can’t flow
- Constant volume

States of Matter

- Liquid
- Particles are tightly packed
- Able to slide past each other
- Can flow
- Constant volume

Liquids

- Spread out on their own
- Fluids- gases and liquids both flow
- Viscosity- the resistance to flow
- The better the molecules stick to each other, the more resistance

States of Matter

- Gas
- Particles are spread out
- Flying all over the place
- Can flow
- Volume of whatevercontainer their in

Gases

- Fill the available space
- Particles moving at about 500 m/s
- Particles hitting things cause pressure

Law of Conservation of Mass

- In all changes, mass cannot be created or destroyed
- All the mass you start with you end with
- It might be hard to count

Law of Conservation of Energy

- In all changes, energy cannot be created or destroyed
- All the energy you put in, you get out
- It might be hard to count

Pressure

- Pressure is the result of collisions of the molecules with the sides of a container.
- Particles in a gas move rapidly in constant random motion.
- They travel in straight paths and move independently of each other.
- As a result, gases fill their containers regardless of the shape and volume

Gas Pressure

- Gas Pressure is the force exerted by a gas over an area
- Gas Pressure is the result of simultaneous collisions of billions of rapidly moving gas particles with an object
- A vacuum is completely empty space - it has no pressure.
- Pressure can be measured with a device called a barometer.

Barometer

- At one atmosphere pressure a column of mercury 760 mm high.

1 atm Pressure

Column of Mercury

Dish of Mercury

Barometer

- At one atmosphere pressure a column of mercury 760 mm high.
- A second unit of pressure is mm Hg
- 1 atm = 760 mm Hg

1 atm Pressure

760 mm

Atmospheric Pressure

- Gas pressure you are familiar with is that caused by a mixture of gases
- The Air
- Air exerts pressure on the Earth because gravity holds air molecules in Earth’s Atmosphere
- Atmospheric Pressure results from the collisions of air molecules with objects.

Units for Pressure

- SI Unit is pascal (Pa)
- We measure in kilopascals (kPa)
- Also:
- Millimeters of mercury (mmHg)
- Standard atmosphere (atm)
- 1 atm = 760 mmHg = 101.3 kPa

Standard Pressure

- Normal atmospheric pressure at sea level.

- It is equal to
- 1.00 atm
- 760 torr (760 mm Hg)
- 101.325 kPa

Conversion Problems

- 1) Tire-pressure gauge records a pressure of 450 kPa. What is the measurement expressed in
- A) atmospheres
- B) millimeters of mercury

Conversion Problem #2

- What is the pressure in Kilopascals and in atmospheres, does a gas exert at 385 mm Hg?

Conversion Problem #3

- The pressure at the top of Mount Everest is 33.7 kPa. Is the pressure greater or less than 0.25atm

Factors Affecting Gas Pressure

- Number of Particles
- Volume
- Temperature

Number of Particles

- Increasing the number of particles will increase the pressure of a gas if the temperature and the volume are constant
- Tire is inflated, volume is fairly constant
- Adding more air will increase the pressure
- More particles with same volume, greater number of collisions
- Greater the pressure
- Tire Explodes

Volume

- Reducing the volume of a gas increases its pressure if the temperature of the gas and the number of particles are constant.
- Relationship between volume and pressure happens when you breathe

Volume Cont.

- Example
- Inhale, diaphragm contracts
- This causes the chest cavity to expand
- Increases the volume, which allows the air particles to expand
- Leads to a decrease in pressure

Volume Cont.

- Exhale, diaphragm relaxes
- Volume of chest cavity decreases
- Particles in the air squeeze into a smaller volume
- Pressure inside your lungs increases

Temperature

- Raising the temperature of a gas increases the pressure if the volume is held constant.
- The molecules hit the walls harder.
- The increase in the number of collisions along with the increase in force of the collisions causes an increase in the pressure
- The only way to increase the temperature at constant pressure is to increase the volume.

Calculating Gas Laws

- Boyle’s Law
- Charles’s Law
- Combined Gas Law

Boyle’s Law

- At a constant temperature pressure and volume are inversely related.
- As one goes up the other goes down
- P x V = K (K is some constant)
- Easier to use P1 x V1=P2 x V2

- As the pressure on a gas increases the volume decreases
- Pressure and volume are inversely related

2 Liters

V

Examples

- A balloon is filled with 25 L of air at 1.0 atm pressure. If the pressure is change to 1.5 atm what is the new volume?
- A balloon is filled with 73 L of air at 1.3 atm pressure. What pressure is needed to change to volume to 43 L?

Charles’ Law

- The volume of a gas is directly proportional to the Kelvin temperature if the pressure is held constant.
- V = K xT (K is some constant)
- V/T= K
- V1/T1= V2/T2

T

Examples

- What is the temperature of a gas that is expanded from 2.5 L at 25ºC to 4.1L at constant pressure.
- What is the final volume of a gas that starts at 8.3 L and 290 K and is heated to 369 K?

Boyle’s & Charles’s Problems

- 1) If I have 45 liters of helium in a balloon at 298K and increase the temperature of the balloon to 328K. What will the new volume of the balloon be?
- 2) My car has an internal volume of 12,000 L. If I drive my car into the river and it implodes, what will be the volume of the gas when the pressure goes from 1.0 atm to 1.4 atm?

More Problems

- 3) If I have 5.6 L of gas in a piston at a pressure of 151.95 kPa and compress the gas until its volume is 4.8 L, what will the new pressure inside the piston be?
- 4) Oxygen gas is at a temperature of 310K when it occupies a volume of 2.3 liters. To what temperature should it be raised to occupy a volume of 6.5 liters?

Gay Lussac’s Law

- The temperature and the pressure of a gas are directly related at constant volume.
- P = K xT (K is some constant)
- P/T= K
- P1/T1= P2/T2

Examples

- What is the pressure inside a 0.250 L can of deodorant that starts at 25ºC and 1.2 atm if the temperature is raised to 100ºC?
- At what temperature will the can above have a pressure of 2.2 atm?

Putting the pieces together

- The Combined Gas Law Deals with the situation where only the number of molecules stays constant.
- (P1 x V1)/T1= (P2 x V2)/T2
- Lets us figure out one thing when two of the others change.

Examples

- A 15 L cylinder of gas at 4.8 atm pressure at 25ºC is heated to 75ºC and compressed to 17 atm. What is the new volume?
- If 6.2 L of gas at 723 mm Hg at 21ºC is compressed to 2.2 L at 4117 mm Hg, what is the temperature of the gas?

Energy

- The ability change or move matter
- As you add energy to a liquid, the temperature goes up
- The molecules move faster
- Eventually they will move fast enough to break free and become a gas
- This is evaporation- the change from a liquid to gas

Evaporation

- Molecules at the surface break away and become gas.
- Only those with enough KE escape
- Evaporation is a cooling process.
- It requires heat.
- Endothermic.

Phases Changes

- If you change rapidly enough, the gas will form below the surface an boil
- Condensation- Change from gas to liquid
- As you cool a gas the molecules slow down
- As gas molecules slow down they stick together

Condensation

- Change from gas to liquid
- Achieves a dynamic equilibrium with vaporization in a closed system.
- What is a closed system?
- A closed system means matter can’t go in or out. (put a cork in it)
- What the heck is a “dynamic equilibrium?”

Phases Changes

- Molecules and atoms don’t change during a phase change
- the composition doesn’t change
- The mass doesn’t change
- The volume does change
- Only the attractions and motion change

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