1. Gas Stoichiometry Unit
Ideal vs. Real Gases
Gas Stoichiometry Unit

2. Gas Law Problems: We have a problem with the gas molecule.
Why is this a problem?
They show attraction! Can’t in Gas
Law Problems
They take up space!!! Can’t in Gas Law Problems
It’s our Physics problem: “Disregard air resistance” How do you do that?

3. Real Gases They do exist. They can liquefy - condensation of vapor.
They don’t follow gas laws.

4. Ideal Gases They don’t exist. They can’t liquiefy.
They follow the gas laws.

5. So when do gases behave ideally so we can use them in our gas laws?
Where they show no attraction to each other:
What conditions would that be?

6. So when do gases behave so we can use them in our gas laws? Ideally
Where they show no attraction to each other:
What conditions would that be?
1) Low pressures
2) High temperatures

7. The building of van der Waal’s equation
Real gases have volume, therefore volume available in container is less. These molecules take up some of the space that we calculated for volume of the container.

8. The building of van der Waal’s equation
Real gases have volume, therefore volume available in container is less. These molecules take up some of the space that we calculated for volume of the container. Correction factor for the Ideal Gas Law P (V-nb) = nRT n= # of moles b=correction factor (pg 224: Table 5.3)

9. The building of van der Waal’s equation
Real gases attract each other (law of universal gravitation), therefore not all of them are colliding with container. Pressure is less than what we calculated it to be.

10. The building of van der Waal’s equation
Real gases attract each other (law of universal gravitation), therefore not all of them are colliding with container. Pressure is less than what we calculated it to be.
Correction factor for the Ideal Gas Law.
(P + a(n/V)2) (V-nb) = nRT
a=pressure correction factor
n/V = amount of gas you have; you increase the amount, you increase the attraction

11. The building of van der Waal’s equation
Johannes van der Waal won the Nobel Prize for his work on this equation in 1910.

12. Van der Waal’s
Calculate the pressure exerted by mol N2 in a L container at 25C,
a) using the ideal gas law
b) using van der Waal’s equation 
c) Compare the results