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

Common Units of Pressure

All of these need to be memorized. Note that the values with the word exactly by them have an infinite number of significant figures. 

Charles' Law

    In Charles' law, pressure and moles are held constant which gives us the formula:

Note: Temperature must be in Kelvin

Example:

     A sample of gas at 15 degrees C and 1 atm has a volume of 2.58L. What volume will this gas occupy at 38 degrees C and 1 atm. 

First, start by listing the known variables. Pressure stays constant, so we do not have to worry about pressure in our calculations. 

• T1= 15 degrees C--> 15 + 273.15 = 288.15 K
• V1= 2.58 L
• V2= ?
• T2= 38 degrees C--> 38 + 273.15 = 311.15 K

Then, plug in the variable into the equation to solve for V2

• V1 x T2 / T1 = V2 
• V2 = (2.58 x 311.15) / 288.15
• V2= 2.79L

Other Gas Laws:

• Boyle's Law
• Avagadro's Law
• Dalton's Law

Air Bag Lab

     Today in class, we had to determine the moles of baking soda and mL of vinegar that would create enough CO2 gas without bursting the bag as a result. Below is the procedure for how we did so.

1. Fill a graduated cylinder with a known amount of water and then pour into the ziplock bag. Repeat this until ziplock bag is full. This value is the volume of the ziplock bag. 

1. Record the pressure and temperature of the room. We were told the temperature was 21 degrees C and the pressure is 29.06 inHg. Then, convert temperature and pressure to Kelvin and atm respectively. Calculaions are shown below.

     3. Use PV=nRT in order to find the moles of CO2. There is a 1:1 molar ratio, so the moles of                  CO2 needed is equal to the moles of NaHCO2 (baking soda). 

     4. Once the number of moles of baking soda and vinegar are found, convert each to g and mL                  respectively. 

Video of a Similar Lab