Chapter 5: Gas Laws & Kinetic Molecular Theory Flashcards
Gas volume changes significantly with pressure but…
solids and liquids are not greatly affected by pressure
Gas volume changes significantly with temperature
gases expand when heated and shrink when cooled; volume change is 50-100 times greater than for liquids or solids
Gases flow very freely and have relatively low densities; gas particles are very far apart and fill available space of their container
Other physical states/properties of gases
Gases form a solution in any proportions
they are freely miscible with each other
Atmospheric pressure arises from the force exerted by atmospheric gases on the earth’s surface
Atmospheric pressure decreases with altitude.
When the pressure of the gas is less than the pressure of the atmosphere, subtract the difference from the total atmospheric pressure
If P(gas) < P(atm): [P(gas) = P(atm) - delta h]
When the pressure of the gas is greater than the pressure of the atmosphere, add the difference to the pressure of the atmosphere
If P(gas) > P(atm): [P(gas) = P(atm) + delta h]
“Ideal gas molecules do not attract or repel each other”–if the interparticle attraction between gas molecules is great enough, the gas will deposit into a liquid or condense into a solid (i.e. dry ice and liquid helium)
AND
“the volume of an ideal gas molecule is negligible compared to the volume of the container”–if this were the case then it would be possible to compress a gas enough so that it does not occupy any volume, which is impossible.
Gases do not always behave ideally in the real world
w = -PdeltaV or w = -nRT
A system that does work on the surroundings has a negative value for ‘work’
A system that has work done on it by the surroundings has a positive value for work
delta V and delta n are positive integers if there is an increase in the # of moles of gas as the reaction proceeds; (P, T, and R always have positive values)
- If a reaction produces more moles of gas than it consumes then:
- deltaV and delta n are positive and Work is negative
- it did work on the surroundings
delta V and delta n are negative if there is a decrease in the # of moles of gas as the reaction proceeds; (P, T and R always have positive values)
- If a reaction consumes more moles of gas than it produces then:
- deltaV and delta n are negative and Work is positive
- it had work done to it by the surroundings
mass =
volume x density
delta T =
T (final) - T (initial)
used to measure the pressure of a gas
manometer
PV = nRT
T = temperature---*always in Kelvin P = pressure--usually in atm or mmHg, also torr n = amount (in moles usually) R = gas constant 0.0821 L*atm/mol*K V = volume
Ideal Gas Law
- can be rearranged in several different ways to find certain values
- ideal gases exhibit linear relationships
- no ideal gas actually exists but most behave nearly this way at ordinary temperature and pressure
mass/volume =
density
mass (g) / molar mass (m/g) =
moles (n)
Molar Mass -
mRT/PV
E = (1/2)m x v^2 = (1/2mass x speed^2) F = ma (force = mass * area)
*At a given T, all gases in a sample have the same average kinetic energy
*Kinetic energy depends on both the mass and speed of the particle
*At a higher mass, gas moves slower (at constant T) and has a lower rate of effusion
(and vice versa)
273.15K, 0*C, 1 atm & 760 mm Hg/torr
STP, Standard Temperature & Pressure
22.41L–the volume of an ideal gas at STP
Standard Molar Volume
[ deltaE(system) + deltE(surroundings) ]
E(universe) =____________________= 0
P1 * V1 / T1 =
P2 * V2 / T2
PV = (mass/molar mass)RT
m/V = d = (molar mass x P) / RT
0.0821 Latm/molK
gas constant R
n = mass/molar mass = PV/RT
molar mass = mRT/PV
gases mix homogeneously in any proportions
-each behaves in a mixture as if it was the only one
pressure of each gas exerted in a mixture =
partial pressure
the total pressure in a mixture is the sum of the partial pressures of all the gases in the mixture
Dalton’s Law of Partial Pressures
partial pressure, X(A) =
n(A )/ n(total)
the partial pressure of a gas is proportional to its mole fraction
the process by which a gas escapes through a small hole in its container into an evacuated space
effusion
the rate of effusion of a gas is inversely proportional to the square root of its molar mass
Graham’s Law of Effusion
rate of eff ~ 1 / root^2(molar mass)
Real gases have real volume
Real gases do experience attractive and repulsive forces between their particles
Real Gases: deviation from ideal behavior
*real gases deviate most at low temperature and high pressure
-50*C / 223-500K / 1-3/5 atm
Gases tend to behave normally over these ranges
