Phases or States
Matter can exist in three different physical forms: solid, liquid, or gas
Gases are called ____ because they can flow
fluids
Gas particles
have weak intermolecular forces between particles; thus they can expand to fill any volume and take the shape of any container. They are also compressible
Gaseous state defined by four variables:
pressure (P) in Pa
volume (V) in mL or L
temperature (T) in K
number of moles (n)
SI unit for pressure
Pascal (Pa)
1 atm = 760 mm Hg = 760 torr = 101.325 Pa
STP conditions
Standard Temperature and Pressure:
273.13 K (0�C) at 1 atm
Ideal Gases
Hypothetical gas whose molecules have no intermolecular forces and occupy no volume
Although real gases deviate from this ideal behavior at high pressures and low temperatures, many real gases demonstrate behavior that is close to ideal
Kinetic Molecular Theory (5 assumptions)
1. Gases are made of particles whose volumes are negligible compared to the container's volume
2. Gas atoms exhibit no intermolecular attractions/repulsions
3. Gas particles are in continuous, random motion
4. Collisions between gas particles are elastic(
Average KE of a gas is proportional to
the absolute temperature of the gas
KE = 1/2 mv^2 = 3/2 kT
m = mass
v = volume
k = Boltzmann constant
T = temperature
root-mean-square speed
This is the average velocity of the gas molecules in a vapor. Found by squaring, averaging, and then Square rooting the velocities of the gas molecules.
R = ideal gas constant
M = molecular mass
T = temperature
Diffusion
The movement of gas molecules through a mixture. Heaver gases move more slowly than lighter ones because of their differing average speeds
Graham's Law
Rate of diffusion of a gas is inversely proportional to the square root of its molecular weight.
Effusion
The flow of gas particles under pressure from one compartment to another through a small opening. Same equation as that for diffusion
Avogadro's Principle
all gases at a constant temperature and pressure occupy volumes that are directly proportional to the number of moles of gas present
Ideal Gas Law
PV = nRT
P = pressure
V = volume
n = number of moles
R = gas constant = 0.0821(L atm/mol K) or 8.314 J/K mol
T = temperature
Density and the Ideal Gas Law
Density = mass/volume (g/L)
n = (mass m/ molar mass M)
PV = (m/M) RT
KE = 1/2 mv^2 = 3/2 kT
Relate changes in temperature, volume, and pressure of a gas
(P1V1)/T1 = (P2V2)/T2
To calculate changes in colume
V2 = V1 (P1/P2) (T1/T2)
V2 can be used to find the density of the gas under nonstandard conditions
d = m/V2
Molar mass
M = d(stp) � V(stp) = d(stp) (22,4 L/mol)
22.4 L/mol is the STP volume of any gas
Boyle's Law
For a given gaseous sample held at constant temperature the volume of the gas is inversely proportional to its pressure. (n, R, and T are constant in ideal gas law)
PV = k or P1V1 = P2V2
k = proportionality constant
Charles Law
V/T = k
V1/T1 = V2/T2
Gay-Lussac Law
P1/T1=P2/T2
Dalton's Law
At constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases
P = p1 + p2 + p3 + ...
P = total pressure
p = partial pressures
Partial Pressure
p = P � X
P = total pressure
X = moles of partial pressure / total moles of all gases
Gases behave closes to ideal gases under
high temperature and low pressure
Deviations due to Pressure
As the pressure of a gas increases, the particles are pushed closer together. As condensation pressure nears for a given temperature, intermolecular attraction forces become more significnat
Deviations due to Temperature
As the temperature of a gas is decreased, the average velocity of the gas molecules decreases and the attractive intermolecular forces become increasingly significant
Van der Waals equation of state
a and b are physical constants experimentally determined for each gas
a = corrects for attractive forces between molecules
b = corrects for volume of the molecules themselves