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- Solid - Molecules are held close to each other by their attractions of charge. They will bend and/or vibrate, but will stay in close proximity.
- Liquid - Molecules will flow or glide over one another, but stay toward the bottom of the container. Motion is a bit more random than that of a solid.
- Gas - Molecules are in continual straightline motion. The kinetic energy of the molecule is greater than the attractive force between them, thus they are much farther apart and move freely of each other.

Nature of Gases

- No definite shape nor volume
- Low density
- Compressibility
- Diffusion

Diffusion

- Which molecules diffuse quicker?
- Heavy, large
- Light, small

Kinetic Molecular Theory

- Gases consist of large numbers of tiny particles that are far apart relative to their size
- Collisions between gas particles and between particles and container walls are elastic (no loss of energy)
- Gas particles are in continuous, rapid, random motion

- There are no forces of attraction between gas particles
- The temperature of gas depends on the average kinetic energy of the gas particles

Pressure

- Force per unit area on a surface
- Pressure =force/ area

- Increase in pressure
- Increase in number of collisions of gas particles

Atmospheric Pressure

- Weight of gases that compose the atmosphere
- 78% nitrogen
- 21% oxygen
- 1% other gases

Ears “pop” in airplane

- Density and pressure of air is lower
- Air pressure inside ears changes to reach same pressure as air in cabin (6,000-8,000 ft above sea level)
- Pressurized
cabin

Measuring Pressure

- Barometer- device to measure atmospheric pressure

Standard pressure

- 760 mm of mercury (760 torr)
- 1 atmosphere (atm)
- 101.3 kilopascals (kPa)

Practice Question

- The average atmospheric pressure in Denver, Colorado is 0.830 atm. Convert this to mm of Hg and kPa.
0.830 atm x 760 mm Hg = 631 mm Hg

1 atm

0.830 atm x 101.3 kPa = 84.1 kPa

1 atm

Gases collected by water displacement

- Gas produced by reaction displaces water which is more dense

Dalton’s Law of Partial Pressure

- Pressure of each gas in a mixture is called partial pressure
- Dalton’s law states that the total pressure of a gas mixture is the sum of the partial pressures of the component gases
PT= P1 + P2 + …

Gas Laws

- Boyle’s Law
- Charles’ Law
- Gay-Lussac’s Law

Boyle’s Law

- Pressure-volume relationship
- Inverse relationship

- PV= k
- P1V1= P2V2
- A sample of oxygen has a volume of 150.0 mL when its pressure is 0.947 atm. What will the volume of the gas be at a pressure of 0.987 atm if the temperature remains constant?
- (0.947 atm)(150.0 mL)=(0.987 atm) V2
- V2= 144 mL

Charles’ Law

- Volume- temperature relationship
- Direct relationship
- V = k
T

- V1 = V2
T1 T2

Always use Kelvin temperature

- A sample of neon gas occupies a volume of 752 mL at 25 degrees Celsius. What volume will the gas occupy at 50 degrees Celsius if the pressure remains constant?
- 752 mL = V2
298 K 323 K

- V2= 815 mL

Gay-Lussac’s Law degrees Celsius. What volume will the gas occupy at 50 degrees Celsius if the pressure remains constant?

- Pressure-temperature relationship
- Direct relationship
- P = k
T

- P1 = P2
T1 T2

Always use Kelvin temperature

- The gas in a container is at a pressure of 3.00 atm at 25 degrees Celsius. What would the gas pressure in the container be at 52 degrees Celsius?
- 3.00 atm = P2
298 K 325 K

- P2= 3.27 atm

Combined Gas Law degrees Celsius. What would the gas pressure in the container be at 52 degrees Celsius?

- If something is constant in the problem, it can be canceled out

- A helium balloon has a volume of 50.0 L at 25 degrees Celsius and 1.08 atm. What volume will it have at 0.855 atm and 10 degrees Celsius.
- (1.08 atm) (50.L) = (0.855 atm)V2
298 K 283 K

V2= 60.0 L

- A sample of helium gas has a volume of 200.0 mL at 0.960 atm. What pressure is needed to reduce the volume at constant temperature to 50.0 mL?
- (0.960 atm)(200.0 mL) = P2 (50.0 mL)
- P2= 3.84 atm

SCUBA atm. What pressure is needed to reduce the volume at constant temperature to 50.0 mL?

- Gas Laws WebQuest

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