# Ch. 10 – Part II - PowerPoint PPT Presentation

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Ch. 10 – Part II. Ideal Gas – is an imaginary gas that conforms perfectly to all the assumptions of the kinetic theory. A gas has 5 assumptions 1. Gases consist of large numbers of tiny particles. 2. The particles of a gas are in constant motion, moving rapidly in all directions.

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Ch. 10 – Part II

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### Ch. 10 – Part II

• Ideal Gas – is an imaginary gas that conforms perfectly to all the assumptions of the kinetic theory.

• A gas has 5 assumptions

• 1. Gases consist of large numbers of tiny particles.

• 2. The particles of a gas are in constant motion, moving rapidly in all directions.

• 3. The average kinetic energy of the particles of a gas is directly proportional to the temp. of a gas.

• KE= ½ MV

• 4. There are no forces of attraction or repulsion between the particles of a gas.

• 5. The collision between particles of a gas and between particles and container walls are elastic collisions.

• Fluid – a gas or liquid

• A gas is about 1/1000 the density of the same substance as a solid or liquid. Why?

• Molecules are farther apart.

• Compression – gas under pressure.

• By compressing a gas you can have as much as 100 times more molecules in a cylinder than uncompressed.

• Effusion – is a process by which gas particles under pressure pass through a very small opening from one container to another.

• What is diffusion?

• Real gas – is a gas that does not behave completely according to the assumptions of the kinetic energy.

• Johannes van der Waals proposed this.

• Real gases are explained by the following:

• 1. Particles of real gases occupy space

• 2. Particles of real gases exert attractive forces on each other.

• Gases behave different when heated, cooled, or under pressure.

• Under “normal conditions” a gas is considered to be an ideal gas.

### Gases have 4 measurable quantities

• 1. Volume

• 2. Pressure

• 3. Temperature

• 4. Quantity of molecules (number)

• If 3 of these quantities are known then you can figure the fourth one.

• If air is heated it can expand its volume many times. If it’s cooled it compresses.

• Pressure is measured by how fast the gas molecules are moving. Determined by how many times the molecules hit the container it is in.

• Ex. Small vs. large container with 10 molecules.

• Temp. increases = pressure increase

• Temp. decreases = pressure decrease

• Volume decreases = pressure increase

• Volume increase = pressure decrease

• The more molecules of gas in a container, the more pressure it has. Why?

• In the winter time the pressure in your car tire is less. Why?

• If you blow up a balloon the volume is constant if the temp. and pressure are constant.

• IDEAL GAS LAW CONSTANT

• R = PV/nT

• Pressure – is the force per unit area on a surface

• P = f/a

• Label  N/cm2 or Pascals

• 1 N/cm2 = 1 Pascal

• The SI unit for force is Newtons (N)

• Barometer – is a device used to measure the atmospheric pressure.

• Torricelli discovered this.

• In a vacuum condition and a sea level a colum of mercury or barometer will rise 760 mm.

• 760 mm of Hg is the atmospheric pressure at sea level and at 0 degrees C.

• 760 mm of Hg = 760 torr. or 1 atm. of pressure

• Sample Problem 10.1

• Standard conditions or STP – standard temperature and pressure.

• 1 atm. Of pressure, 760 torr., or 760 mm Hg  Pressure

• 273 K or 0 degrees Celsius  Temperature

• 1 Liter or 1000 ml  Volume

• Robert Boyle discovered that pressure and volume are inversely proportional to each other.

• Ex. Double the volume = ½ the pressure

• Ex. Triple the pressure = 1/3 the volume

• Ex. Pushing in on the sides of a balloon increases the pressure of the air inside the balloon.

• P1V1 = P2V2

• Sample Problem 10-2

• Charles’ Law – states that the volume of a gas varies directly to the temperature of the gas.

• Ex. Double the temp. = double the volume

• Ex. Hot air balloon

• V1/T1 = V2/T2

• Sample Problem 10-3

• Gay-Lussac’s Law – states that the pressure of a gas is directly proportional to the temp. of the gas.

• Ex. Double temp. = double the pressure

• Ex. Car tires

• P1/T1 = P2/T2

• Sample Problem 10-4

• Combined gas law – shows the relationship between pressure, volume, and temp. of a gas when the amount of gas is fixed.

• P1V1/T1 = P2V2/T2

• Sample Problems