The Ideal Gas Law

Objectives:

1.    State the ideal gas law and describe its variables.

2.    Describe the conditions in which the behavior of a real gas varies from that of an ideal gas.

Key Terms:

Ideal gas    real gas    gas constant

Notes: (13-4)

As we learned in the last lecture, the gas laws of Boyle, Charles, Avogadro, and Dalton merely explain the Kinetic-Molecular theory.  Each of the gas laws attempted to isolate situations where two of the four gas variables (T,V,P,&n) were related to each other in controlled conditions.  As you know, life does not always come in such neat controlled packages.  The ideal gas law attempts to combine all of the situational variables and express them in one single equation.

The Ideal Gas Law:

The ideal gas law attempts to describe the behavior of real gases under ideal conditions.  Although most gases adhere to the ideal gas laws there are instances were they don't.

 Very high pressures - distance between the molecules becomes too small and volume is no longer negligible Very low temperatures - kinetic energy of the molecules drops and attractive forces between the molecules increases

Ideal Gas Formula:        PV = nRT            or        P1V1/nRT1 =  P2V2/nRT2

In the above equation the new variable R is the gas constant (0.0821 atm-L/mol-K).  The value R is sometimes the universal gas constant and is used to predict the behavior of ideal gases.