Chapter 6 - Gases Flashcards
What are the 7 main proportie of gas?
- 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
What is pressure?
- 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
What is a barometer?
- 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
What is a manometer?
Manometers measure gas pressure inside a flask relative to atmospheric pressure
What is Boyle’s Law?
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
What are ideal gases?
They strictly obey all gas laws
- volumeless
- strike each other with elastic collisions (like pool
balls)
- have no attraction to one another
What are real gases?
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
What is Charles’ Law?
- 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
What is Avogadro’s Law?
- 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
What is the Ideal Gas Law?
- The behavior of a gas is governed by four
variables, any of which can be calculated if the
other three are known - PV = nRT
What is R?
The universal gas constant
- R = 0.08206 Latm/Kmol
what is STP?
Standard temperature and pressure, 0C and 1 atm
What is molar volume?
- 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
How can molar mass and density be calculated?
They can be calculated from PV = nRT
- PV = mass/molar massRT
- molar mass = mass/PVRT
- d(density) = mass/V
- molar mass = dRT/P
What is Dalton’s Law?
- 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
What does a gas always contain when it is collected over water?
It always contains a small amount of water vapor
- Subtract the vapor pressure of water from the
total pressure
What is kinetic energy?
- 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
What is the relationship between temperature and kinetic energy?
- 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
What is root mean square velocity?
- 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
What is diffusion?
The mixing of gases
What is effusion?
Movement of a gas through a pinhole into an evacuated chamber
What is Graham’s law of effusion?
- 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
What is van der Waals equation?
- 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
- gases with weak intermolecular forces have
- b subtracts the volume of gas molecules
themselves
- generally increases with the size of the gas
particle
