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

The Ideal Gas Law• The ideal gas law attempts to describe the behavior of real

gases under ideal conditions.• Ideal Gas Formula: PV = nRT or P1V1/nRT1 = P2V2/nRT2

• R is the gas constant (0.0821 atm-L/mol-K or 8.31kPa-L/mol-K ). – The value R is sometimes the universal gas constant and is used to predict the behavior

of ideal gases.

• Example: A sample of pure nitrogen gas exerts a pressure of 1 atm. When cooled to a temperature of 0oC it has a volume of 2L. How many moles of gas are present in the sample?

Exceptions to Dalton’s Law

• 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