Gases Flashcards
macroscopic level of gases
properties
molecular level of gases
- structure
- dynamics (motion)
- intermolecular forces
equation and definition for pressure
P=F/A
= force exerted per area
SI units for pressure
Pa = N/m^2
kPa=10^3 Pa
1atm =
101.3 kPa, 760mmHg (Torr)
1 bar =
100.0 kPa
equation for pressure with density, g, and h
p x h x g, where g = 9.8m/s^2
what does the manometer lead to?
an equalisation of pressure:
P(atm) = P(Hg) = p(Hg)gh(Hg)
if the Hg in a manometer was replaced with water, would the height of the water be greater or less than Hg?
greater, due to water’s lower density (P constant, p goes down, g constant, so h goes up)
describe kinetic molecular theory - the ideal gas
- gases made of tiny particles moving completely randomly
- total volume of particles very small compared to size of container
- particles do not interact with each other
- particle collisions are elastic (no energy lost)
- kinetic energy (KE) increases with temperature
describe (5) KE increases with temperature
for a large collection of molecules:
- at a given temperature, all gases have the same distribution of kinetic energy
- each molecule: KE = 1/2mv^2
what is the effect of temperature on average kinetic energy?
the average kinetic energy increases with temperature
state 2 equations relating kinetic energy with temperature
KE(avg) = 3RT/2
Temperature is in Kelvin
KE is in J/mol
KE (avg) = 3RT/2Na
for a single gas molecule
units for R
J/molK
3RT/2Na =
1/2mu^2
state the 2 equations relating u, R, T, m, Na, and M
how is kinetic energy dependent on the mass of the particles?
at the same temperature, more massive molecules move slower
what does pressure result from?
gas particles colliding with container walls
Boyle’s law
at constant T and fixed n, volume is inversely proportional to pressure, or V=k/P
low Pext = Pgas
-> high V
high Pext = Pgas
-> low V
Charles Law
at same P and fixed n, volume is proportional to temperature, or V= kT
Avogadro’s law
V=kn
what equation describes an ideal gas?
PV = nRT
P - atm
V - L
T - K
P1V1/n1T1 =
P2V2/n2T2
mole fraction of gas A
Xa = na/ntotal = Pa/Ptotal
law of partial pressures
Pa + Pb + Pc +…. = PTotal
PA = XA × Ptotal
define effusion
escape of a pas through a hole into a vacuum
define diffusion
movement of one gas through another
how does a barometer work?
The mercury column in the mercury barometer stays up due to the force exerted by the atmosphere on the mercury
in the outer reservoir just balancing the gravitational force on the mercury in the tube. Its height adjusts according
to the air pressure on the reservoir. The column of mercury is shorter on a mountaintop as there is less atmosphere
to exert a force on the mercury reservoir. On a mountaintop, the air pressure is less, so the height of mercury it
balances in the barometer is shorter than at sea level where there is more air pressure
