The Gas Phase Flashcards
Gases are classified as fluid because they…
can flow into and tke the shape of whatever container
Gasses are different from liquids as…
very low intermolecular forces between gas particles
molecules move very rapidly and are far apart
and compressible
1 atm =
760 torr
760 mmHg
101.325 kPa
Sphygamomanometers
medical devices which meaure blood pressure
How Barometers Work
atmospheric pressure creates downward force on mercury which exerts upward force creating a vacumn
when air exerts greater force than weight of mercury, it goes up
when air exerts lesser force than weight of mercury, it goes down
STP vs Standard State
1 atm 273 K
1 atm, 273K , 1 M
Ideal Gas
a gas whose molecules have no inter molecular forces and occupy no volume
real gases deviate from this at high/low pressures (low/high volumes)
Ideal Gas Law
PV=nRT
R = 8.21*10^-2
Ideal Gas Law With Density
p = m/V = PM/RT
Combined Gas Law
used to relate changes in temperature, volume and pressure.
P1V1/T1 = P2V2/T2
Determining Molar Mass of Gas at STP
1) Determine mass of sample at the given temp/pressure
2) Find density of sample given the volume
3) find volume at STP using combined gas law and STP conditions
4) Density at STP is sample mass divided by volume at STP found
5) find molar mass by multiplying the density calculated and volume of STP of 1 mole gas ( 22.4 L/mol)
mm = p STP * 22.4 L/mol
Avogadro Principle
all gases at constant temperature and pressure occupy volumes that are directly proportional to the number of moles of gas present
n/V = k or n1/v1 = n2/V2
Boyles Law
P1V1 = P2V2 pr PV = k
gas sample held at constant temperature (isothermal) volume is inversely proportional to its pressure
Boyles Law Isothermal Compression
As pressure increases, volume decreases
Charles Law
at constant pressure (and moles), the colume of a gas is proportional to its temperature in kelvin
V1/T1 = V2/T2
Charles Law (Isobaric Expansion)
as temperature increases, so does volume
Gay-Lussacs Law
likes Charles but relates pressure and temperature where volume and moles are constant
P1/T1 = P2/T2
Gay-Lissacs Law (Isovolumetirc Heating)
as temperature increases, so too does pressure
When two or more gases that do not chemically interact are in one vessesl they will _______. Therefore the pressure exerted by each gas is equal to the pressure that the gas would exert if _____ Pressure exerted by each gas is known as a ______
behave independently of each other
it were the only one in the container
partial pressure
Daltons Law of Partial Pressures
Total pressure of gasseous mixture is equal to the sum of all partial pressures
PT = Pa+Pb+Pc+….
Mole Fractions and Partial Pressures
Pa = Xa * PT
Xa = moles of a / total moles of gas
Vapor Pressure
pressure exerted by evaporated particles above the surface of a liquid
the concentration of a gas in liquid can change depending on the applied pressure
[a] =kH * Pa or [a1]/P1 = [a2]/P2 =kH
kH = henrys constant
[a] = concentration of gas
Assumptions of Kinetic Molecular Theory
1) gases are made of particles with volumes negligible to container volume
2) gas atoms/molecules have no intermolecular forces
3) gas particles have random motions
4) collisions between any two gas particles are elastic (concervation of momentum and KE)
5) avg kinetic energy is proportional to temperature of gas
Avg Gas Kinetic Energy
KE = 1/2mv^2 = 3/2kBY
kB = Boltzmann Constant (1.38*10^-23)
speed of moleculae is propotional to its temperature
Avg Gas Molecular Speeds
Root-mean square speed
= sqrt ( (3RT)/mm )
R = ideal gas constant mm = molar mass
Maxwell-Boltzmann Distribution Curve
curves of molecular speed of gas molecules at different temperatures
as temp increases, number of molecules at faster speeds increases
The kinetic molecular theory of gasses predicts that ____ gases diffuse more _____ than ____ ones due to differing avg. speeds. This is because all gas particles have same avg. KE at same temperature.
heavier
slowly
lighter
Grahams Law
r1/r2 = sqrt( mm2/mm1)
under isothermal and isobaric conditions, the rates at which two gases diffuse are inversely proportional to the sqrt of their molar masses
Effusion
flow of gas particles under pressure from one compartment to another through a small opening
Real gases deviate from ideal gas behavior to some extent when gas atoms/molecules are _____ under high pressure at low volume or low temperature.
forced into close proximity
At extremely high pressures, size of particles become _____ compared to distance between them so a LARGER volume is taken up and ____ can never be met.
At moderately high pressure, a gas volume is _____ than predicted ideal gas law due to intramolecular attraction
relatively larger
0
less
As the ______ pressure for a given temp is approached, _____ forces become more significant until the gas ____ into a liquid.
condensation
intramolecular
condenses
As the temperature of a gas _____, the avg speed of a gas decreases and the attractive forces become ____
decreases, significant
The closer a gas is to its ______ point, the less ideally it acts. It will have a ____ volume than predicted.
At extremely low temperatures , gas will occupy ______ space than predicted
boiling point, smaller
more
van der Waals Equation of States
(P + (N^2 a)/V^2) (V-nb) = nRT
a and b are physical constants experimentally determined
a - attractive forces between molecules (larger polar ones have high value)
b - volume of molecules themselves
