1. Diffusion, STP, and Ideal Gas Law

2. Diffusion
What happens if I release open a container filled with green gas?
Diffusion – movement of particles
from a region of higher density to a
region of lower density; this is caused by the random motion of molecules

3. Dalton’s law of partial pressures
Dalton’s Law of Partial Pressure – the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases
Ptotal = PA + PB + PC … B A C
In this cylinder, which type of gas molecule will have the highest partial pressure? A A A B B C B A A B
Molecule A C

4. Practice Partial pressures
If the partial pressure of A is 6 atm (PA = 6), the partial pressure of B is 5 atm (PB = 5), and the partial pressure of C is 3 atm (PC = 3), what is the total pressure of the container?

5. Derive ideal gas law Variables Pressure Temperature Volume
Number of Molecules (Moles)
What happens to the pressure when we change these?
Increase Temperature = Increase Pressure
Increase Volume= Decrease Pressure
Increase Moles = Increase Pressure

6. Ideal gas law
Ideal Gas – gas in which molecules keep the exact same speed after collisions. In other words, friction does not slow them down
Can approximate most gases as ideal
PV = nRT
P = Pressure
V = Volume
n = number of moles
R = Ideal Gas Constant
T = temperature

7. Ideal gas constant
R = Ideal Gas Constant
R = 8.314
R =

8. Review: celsius and kelvin
Celsius to Kelvin
TK = TC + 273
Kelvin to Celsius
Tc = TK - 273
The temperature in Kelvin is always bigger than the temperature in Celsius!!
TK > TC

9. Standard temperature and pressure
Because gases are easily affected by temperature and pressure changes, we need a standard pressure and temperature to refer to
Standard Temperature and Pressure (STP)
Temperature = 0 degrees C
Pressure = 1 atm

10. Standard Temperature and Pressure & Ideal gas law
Let’s use PV=nRT to find the volume of mol of an ideal gas at STP.
P = 1 atm
V = ?
n = 1.00 mol
R =
T = 0 degrees celsius Kelvin = 273 Kelvin

11. More ideal gas Problems
What pressure has a container with 1.20 moles of gas, L, and 25 degrees Celsius?

12. More Ideal Gas Problems
A balloon has a volume of 15.9 L, 149 kPa, and a temperature of 28 degrees C. How many moles of gas are in the balloon?