The most important conditions of gases are volume, pressure, temperature, and molar amount. You can understand that the nature of a gas heavily depends upon the conditions under which it exists.
V & P (INVERSELY proportional). When pressure is doubled, the volume is halved. (Boyle's Law).
x2 P, 1/2 V
x2 V, 1/2 P
V & T (DIRECTLY proportional), why a gas contracts when cooled and expands when heated, ex: hot-air balloon (Charles' Law).
GAS LAW PROBELMS MUST ALWAYS BE DONE WITH TEMPERATURE ON THE KELVIN SCALE!!!!!!!!!! +273
Avogadro: two gases under the same atmospheric condition, STP, must have the same number of moles of gas (n).
Avogadro: two gases under the same atmospheric condition, STP, must have the same number of moles of gas (n).
“It is assumed that molecules in an IDEAL GAS have NO VOLUME and that there are NO INTERACTIONS between the molecules.”
From all this we derive the ideal gas law, the king shiz of all gas laws, PV = nRT.
exam:
P of gas increases when "n" number of molecules increases
- meaning # of molecules increases
- to find # of molecules of a gas in 25 gram sample, divide the "molar mass of the gas" into 25 g...
1 mol gas = 22.4 L (volume of space!)
What about the density of a gas? Don't forget that D = m/v. Since density depends on volume and the volume of a gas varies with temperature and pressure, the density of gas ALSO varies with temperature and pressure.
Of note: Density of a gas is directly proportional to its molecular weight. Bromine is 5x heavier than oxygen. Bromine gas (a reddish brown stink-o-maticks) is 5x denser than oxygen!!
Dalton, being the partial guy that he is, went on to say that the pressure exerted by a gas is the sum of all its partial pressures. (P = P1 + P2 + P3...)
The Kinetic-Molecular Theory: gas pressure is the result of the bombardment of the container walls by constantly moving molecules.
- PRESSURE all depends on the NUMBER of gas molecules in a container, related to how FAST they're moving (frequency of collisions).
- Altering the volume or temperature of a gas in a container will invariably alter its pressure and therefore, kinetics.
Effusion
Graham's Law: rate of effusion is inversely proportional to the square root of the molecular weight... wah?
- the heavier the gas, the slower it will diffuse! (think of how slowly the fat kid diffuses through la cancha on field day...)
What about the density of a gas? Don't forget that D = m/v. Since density depends on volume and the volume of a gas varies with temperature and pressure, the density of gas ALSO varies with temperature and pressure.
Of note: Density of a gas is directly proportional to its molecular weight. Bromine is 5x heavier than oxygen. Bromine gas (a reddish brown stink-o-maticks) is 5x denser than oxygen!!
Dalton, being the partial guy that he is, went on to say that the pressure exerted by a gas is the sum of all its partial pressures. (P = P1 + P2 + P3...)
The Kinetic-Molecular Theory: gas pressure is the result of the bombardment of the container walls by constantly moving molecules.
- PRESSURE all depends on the NUMBER of gas molecules in a container, related to how FAST they're moving (frequency of collisions).
- Altering the volume or temperature of a gas in a container will invariably alter its pressure and therefore, kinetics.
Effusion
Graham's Law: rate of effusion is inversely proportional to the square root of the molecular weight... wah?
- the heavier the gas, the slower it will diffuse! (think of how slowly the fat kid diffuses through la cancha on field day...)
ra x Ma½ = rb x Mb½
rate of 2 gases effusing together: (Mb/Ma)½
Rate is always expressed as (1/unit time)!
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