Gas Laws

There are two types of gas equations. One is the class of equations describing a what happens when a gas changes from one condition to another. The second class of equations describe a single state where NO changes occur.

Single state equations- no changes

Dalton's law

Ptotal = P1 + P2 + P3....

Universal gas law

PV = nRT

Gas density at STP, grams / Liter

density = d = molar mass/ 22.4 L

Change of state equations- Two states or conditions exist, both an initial and final state

Boyle's law

P1V1 = P2V2

constant T and moles

Charle's law

V1/T1 = V2 /T2

constant P and moles

Gay-Lussac's law

P1/T1 = P2 /T2

constant V and moles

Combined gas law

P1V1/T1 = P2V2 /T2

constant moles

Avogadro's law

n1/V1 = n2/V2

constant T and P

All these equations follow assumptions of the kinetic molecular theory for gases.

Standard temperature and pressure, STP

From the preceding equations it should be clear that gas properties change with temperature and pressure. A standard reference condition has been defined so comparisons of gases can be made. A reference standard temperature and pressure, are set at STP, 273.16o Kelvin and 1 atmosphere pressure.

Molar volume at STP

All gases at STP have the same molar volume, 22.4 Liters. This naturally comes about when the Ideal / Perfect Gas law is used to calculate volume for 1 mole at STP.


Dr. Walt Volland, all rights reserved 1998-2005

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