Chapter 6 - Gases

Question 1

What are the 7 main proportie of gas?

Answer 1

• No fixed volume, expand to fill their container
• No fixed shape, take the shape of container
• Highly compressible
• Mix completely with other gases
• Exert pressure on their surroundings
• Very low density
• Fluid, flow from high to low pressure

Question 2

What is pressure?

Answer 2

• Force per unit area
• The SI unit of pressure is the pascal (PA)
  
  • 1 Pa = 1 N/m^2 = 1 kg/(m*s^2)
• Torrs and standard atmospheres (atm) are not SI
  units

Question 3

What is a barometer?

Answer 3

• Barometers measure atmospheric pressure
• The first barometer was a tube of Hg inverted
  into a bowl
• At sea level, the Hg column is 760 mm

Question 4

What is a manometer?

Answer 4

Manometers measure gas pressure inside a flask relative to atmospheric pressure

Question 5

What is Boyle’s Law?

Answer 5

At constant temperature and moles the pressure and volume of a gas are inversely proportional
- PV = k
- P1V1 = P2V2
- Gas pressure is a result of the particles striking
their container. As pressure increases, the
particles collide with the container more often

Question 6

What are ideal gases?

Answer 6

They strictly obey all gas laws
- volumeless
- strike each other with elastic collisions (like pool
balls)
- have no attraction to one another

Question 7

What are real gases?

Answer 7

They best obey gas laws at low pressures and high temperatures
- Low P: the particles’ volume is less significant
- High T: high KE avg makes collisions more elastic

Question 8

What is Charles’ Law?

Answer 8

• At constant pressure and moles, volume and
  temperature are directly proportional
• Like all matter, gases expand when heated
• Sealed cylinders with pistons and tied balloons
  demonstrate this law because P and n are
  constant
• V = bT
• V1/T1 = V2/T2

Question 9

What is Avogadro’s Law?

Answer 9

• V = an
• V1/n1 = V2/n2
• Inflating a balloon or adding gas to a cylinder
  with a moveable piston demonstrates
  Avogadro’s Law
• For these objects (at constant P and T) adding
  more moles of gas increases volume

Question 10

What is the Ideal Gas Law?

Answer 10

• The behavior of a gas is governed by four
  variables, any of which can be calculated if the
  other three are known
• PV = nRT

Question 11

What is R?

Answer 11

The universal gas constant
- R = 0.08206 Latm/Kmol

Question 12

what is STP?

Answer 12

Standard temperature and pressure, 0C and 1 atm

Question 13

What is molar volume?

Answer 13

• The volume of one mol of a gas
• The molar volume of an ideal gas at STP is 22.42
  L
• V = 1 mol0.08206273.15K / 1 atm = 22.42 L

Question 14

How can molar mass and density be calculated?

Answer 14

They can be calculated from PV = nRT
- PV = mass/molar massRT
- molar mass = mass/PVRT
- d(density) = mass/V
- molar mass = dRT/P

Question 15

What is Dalton’s Law?

Answer 15

• For gas mixtures, the total pressure is the sum of
  the pressures each gas would exert by itself
• Ptotal = P1 + P2 + P3 + …
• P1/Ptotal = n1/n total

Question 16

What does a gas always contain when it is collected over water?

Answer 16

It always contains a small amount of water vapor
- Subtract the vapor pressure of water from the
total pressure

Question 17

What is kinetic energy?

Answer 17

• Gas particles frequently collide and exchange
  kinetic energy
• A sample of gas at a given temperature has
  particles with a wide range of velocities
• At higher T, these ranges become very broad

Question 18

What is the relationship between temperature and kinetic energy?

Answer 18

• Temperature is a measure of average kinetic
  energy
• This equation provides the KE avg of a mole of gas particles at a given temperature
• KE ave = 3/2*RT

Question 19

What is root mean square velocity?

Answer 19

• u rms is the average speed of particles in a
  sample of gas
• units are in m/s
• u rms = sqrt(3RT/M*M)
• MM = molar mass in kg
• the kinetic energy of an object in motion is its
  mass times its velocity squared
• average kinetic energy is directly proportional to
  Kelvin temperature

Question 20

What is diffusion?

Answer 20

The mixing of gases

Question 21

What is effusion?

Answer 21

Movement of a gas through a pinhole into an evacuated chamber

Question 22

What is Graham’s law of effusion?

Answer 22

• At the same temperature and pressure, the
  relative rates of effusion of two gases are given
  by the equation
• effusion rate for gas 1 / effusion rate for gas 2
  = sqrt(MM2) / sqet(MM1)
• Lower molar mass, lighter gas particles, higher
  velocities, faster effusion

Question 23

What is van der Waals equation?

Answer 23

• The ideal gas law was adjusted to the van der
  Waals equation to describe real gas behavior
  more accurately
• P + a(n/V)2 * (V - nb) = nRT
• P corrected for intermolecular forces
• V corrected for gas volume
• a accounts for interactions among gas particles
  
  • gases with weak intermolecular forces have
    low values of a
• b subtracts the volume of gas molecules
  themselves
  - generally increases with the size of the gas
  particle