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chem200 gases cheat sheet to use when studying
Gas Laws
Boyle's Law |
PinitialVinitial=PfinalVfinal |
Charles's Law |
Vi÷Ti = Vf÷Tf |
Combined Gas Law |
PiVi÷Ti = PfVf÷Tf |
Avogadro's Law |
Vi÷ni=Vf÷nf |
Ideal Gas Law |
PV=nRT |
Dalton's Law of Partial Pressure |
Ptotal=P1+P2+P3... |
Dalton's Law of Partial Pressure
Partial Pressure |
Pgas(atm)=(total pressure x molesgas)÷total moles |
PP when volumes are different |
Ptotal=P1(atmxV1÷Vtotal)+P2(atmxV2÷Vtotal)... |
Mole fraction |
moles of gas ÷ total moles |
Wet Gas |
Pwet gas=Ptotal-PH2O |
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then use PV=nRT to solve for variables |
Real Gases
Van der waal's equation |
P=[(nRT)÷(V-nb)] - [(a*n2)÷(V2)] |
When comparing real gases |
a gas with a larger "a" value will require the largest correction to account for intermolecular forces |
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a gas with a smaller "b" value will behave most ideally at high pressures |
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If Vdw's pressure is lower than the ideal pressure, attractive forces dominate |
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If Vdw's pressure is higher than ideal pressure, repulsive forces dominate |
Real Gas Behavior |
attractive forces between molecules cause a decrease in pressure |
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As molecules increase in size deviations from ideal behavior become apparent at relatively HIGH temps |
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In general, most gases behave most ideally at HIGH temps and LOW pressures |
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Pressure Units and Conversions
1 atm= |
1 atm (R= .08206) |
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760 mmHg (R= 62.364) |
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760 torr |
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1.013x105 Pa |
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101.3 kPa |
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29.92 inches Hg |
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14.69 psi |
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1.01325 bar |
Stoichiometry and Gases
Mole ratio = Volume ratio |
2A+3B=AB |
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2A:3B |
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2mL A:3mL B |
Kinetic Molecular Theory
Temperature |
If temperature is increased, Pressure and KE increase by a factor of Tf÷Ti and rms increases by a factor of √Tf÷Ti |
Volume |
If volume is increased, Pressure increases by a factor of Vi÷Vf while KE and rms increase by a factor of 1 (because they are not affected)) |
Moles |
If moles are increased, pressure increases by a factor of nf÷ni, while KE and rms increase by a factor of 1 (no change) |
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Using Ideal Gas Law to Calculate Gas Properties
Ideal Gas Law |
PV=nRT |
STP |
0 degrees celcius, 273 degrees Kelvin, 1 atm, 22.4 L/mol |
Density |
d=MP÷RT where M is molar mass |
Volume |
When not given volume, but told to assume ideal gas behavior, use V=1L |
Diffusion and Effusion
G1=gas 1 |
G2=gas 2 |
Average Kinetic Energy |
KEG1 = KEG2 when TG1=TG2 |
Molecular Speed |
√u2 = √3RT÷M where M is the molar mass |
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√u2G1 ÷ √u2G2 = √MG2 ÷ √MG1 |
Rate |
d/dx G1 ÷ d/dx G2 = √MG2 ÷ √MG1 |
Time |
tG2 ÷ tG1 = √MG2 ÷ √MG1 |
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