Ideal Gas Law

Note: Pressure must be in atm, volume must be in L, and 

temperature must be in K. The constant R is .0821 L atm/ mol K. 

Modeled on the Kinetic Theory of Gases which has 4 basic postulates:

• Gases consist of molecules which are in continuous random motion
• The volume of the molecules present is negligible compared to the total volume occupied by the gas
• Intermolecular forces are neglibible
• Pressure is due to the gas molecules colliding with the walls of the container

Example: Calculate the volume (L) occupied by 7.40 g NH3 at STP. 

First, list the knowns. 

• V= ?
• T=273.15K
• P= 1.00 atm
• n= 7.40 g x (1 mol/17.04g) = .434 g
• R=.0821

Then, plug in the values into the equation to solve for V. 

• PV=nRT
• 1.00V=.434 x .0821 x 273.15
• V = 9.73 L 

Ideal Gas Law Video