Chapter 5 – Gases
Kinetic Molecular Theory (KMT)
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Distances between particles are so small they are assumed to be negligible.
Particles are in constant motion therefore collisions are the cause of pressure.
Particles do not attract or repel each other.
Average kinetic energy of gas particles is directly proportional to its Kelvin temperature.
STP= standard temperature and pressure (273K=0°c and 1 atm)
*at STP 1 mol of gas has volume of 22.4 L
Boyle’s Law 
P₁V₁=P₂V₂
Volume of gas at constant temperature varies inversely with pressure.
Charles’ Law - V₁/T₁=V₂/T₂
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Volume of sample of gas at constant pressure is directly proportional to temperature in Kelvin’s.
Avogadro’s Law - V₁/n₁=V₂/n₂
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Equal volume of gases at same temperature and pressure have same number of particles.
Gay-Lussac’s Law - P₁/T₁=P₂/T₂
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Pressure of a fixed mass of gas at constant volume varies directly with the Kelvin temperature.
Combined Gas Law - P₁V₁/T₁n₁=P₂V₂/T₂n₂
Ideal Gas Law - PV=nRT
P=pressure (atm) where 760 torr=760mmHg=1atm
v= volume (L)
T=temperature (Kelvin) where K=°c+273
R= 0.0821 L·atm/(mol·K)
n=moles (mol)
Other Form of Equation - PV=(m/μ)RT
m=mass (g)
μ=molar mass (g/mol)
Density Form of Equation - D=Pμ/RT (g/L)
Dalton’s Law of Partial Pressure - Ptotal = Pa+Pb+Pc...
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For a mixture of gases in a container, the total pressure exerted is the sum of the pressure of
each gas if it were alone.
Mole Fraction - Xa = na/ntotal = Pa/Ptotal
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The ratio of the number of moles of a given component to the total number of moles.
Gas Collection Over Water - Ptotal = Pgas+Pvh2o
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Total pressure is equal to pressure of gas plus the pressure of water vapor.
Math for Gas Molecules - KE=(3/2)RT
KE units = J/Mol
R= 8.31 J/mol·K
Root Mean Square Velocity - Square Root of (3kT/m) or Square Root of (3RT/μ)
r= 8.31 J/mol·K
k= 1.381x10^-23 J/K Boltzmann’s Constant
Urms units = m/s
m=mass (kg)
μ= molar mass (kg/mol)
Diffusion - the mixing of gases
equation : r₁/r₂ = square root of (μ₂/μ₁)
where r = rate in units of volume / time
Effusion - passage of gas through a tiny opening
same equation as diffusion