1. Combined Gas Law
When the three different laws just discussed are analyzed, what would they be if they are all combined?
PV = k1
V/T=k2
P/T = k3

2. Combined Gas Law PV/T = k4
If the number of moles remains constant, we can solve for any of the other variables
P1V1/T1= P2V2/T2
Also used is Standard Temperature and Pressure (STP)
Standard Temperature is 0oC
Standard Pressure is 1.00atm

3. Combined Gas Law
At a pressure of torr and 24.2oC, Xenon has a volume of 0.350L. What will the volume be at STP?
First change temperature to Kelvin
24.2oC = K
P1V1/T1= P2V2/T2
(780.0torr)(0.350 L)/(297.2K) = (760.0torr)V2/(273K)
V2 = L

4. Diffusion and Effusion
Diffusion is the movement of particles from high density to low density
Popping a balloon
Effusion is the passage of gas molecules under pressure through a tiny opening
Nail in a tire

5. Graham’s Law of Diffusion
In Graham’s Law of Diffusion, we will analyze the kinetic energy of two different gases
Kinetic energy formula is 1/2mv2
m is the mass (in this case molar mass)
v is the velocity of the molecule
Graham’s Law states that the kinetic energy of the first gas will equal the kinetic energy of the second gas
m1v12= m2v22

6. Graham’s Law of Diffusion
Oxygen molecules have an average speed of 480 m/s at room temperature. At the same temperature, what is the average speed of molecules of sulfur hexafluoride?
Molar mass of Oxygen is g/mol (O2)
Molar mass of SF6 is g/mol
m1v12= m2v22
(32.00 g/mol)(480 m/s)2= ( g/mol) v2
v = 224 m/s

7. Dalton’s Law of Partial Pressures
Dalton’s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of each gas
PT = P1 + P2 + P3 + ……
A 42.0 mL sample of hydrogen is collected over water at 30.0oC. What is the total pressure if the pressure of the dry gas torr and the vapor pressure of water at 30.0oC is 18.6 torr?
PT = torr torr
PT = torr