1. Chapter 11 - Gases

2. POINT > Use KMT to explain how gases exert pressure on a container
POINT > Define atmospheric pressure
POINT > Describe how a barometer is used to determine atmospheric pressure
POINT > Identify common units of gas pressure
POINT > Explain Partial Pressures (Dalton’s Law)

3. POINT > Use KMT to explain how gases exert pressure on a container
Recall that KMT tells us that gas particles are in constant random motion
So gas particles are continually hitting the inner surface of the vessel. This creates pressure

4. WB CHECK:
What assumption of Kinetic Molecular Theory explains why gases exert pressure on their surroundings?

5. POINT > Define atmospheric pressure
Pressure is defined as force per unit area
ex. pounds per square inch (PSI)
Atmospheric pressure is the pressure exerted by the gases in our atmosphere, which is ~ 18 km high
The SI unit of force is the Newton (N) defined as kg∙m/s2
Atmospheric pressure exerts a force of about 10N/cm2

6. WB CHECK:
How is pressure defined?

7. POINT > Describe how a barometer is used to determine atmospheric pressure
Atmospheric pressure can be measured with a barometer, invented by Evangelista Torricelli in the 17th century
A barometer indicates atmospheric pressure by showing how high the pressure can raise a column of liquid, traditionally mercury (Hg)

8. POINT > Describe how a barometer is used to determine atmospheric pressure

9. POINT > Describe how a barometer is used to determine atmospheric pressure
At sea level and 0C (STP), the Hg column is raised 760 mm
As atmospheric pressure goes
up or down, the column of Hg
adjusts accordingly

10. WB CHECK:
How high does mercury go in a barometer at STP?
Who invented the barometer?

11. POINT > Identify common units of gas pressure
One common unit of pressure is mm Hg and 1 mmHg is called 1 torr
760 mm Hg (or 760 torr) = 1 atmosphere (atm) = 1 bar
To complicate matters, Frenchman Blaise Pascal was also doing gas research in the 1600’s and another unit of gas pressure is the Pascal (Pa) or kPa
1 atm = 101.3kPa = 1 bar

12. WB CHECK:
What are 4 units of gas pressure?

13. POINT > Explain Partial Pressures (Dalton’s Law)
We often are interested in volumes that contain mixtures of gases
The air we breathe: ~ 78% N2, 21% O2, <1% Ar, <1% H2O
The pressure of a gas mixture is the sum of the pressure exerted by each gas by itself. This is the partial pressure of each gas

14. POINT > Explain Partial Pressures (Dalton’s Law)
This makes sense in terms of KMT assumptions:
“The particles in a gas do not interact”
So, each gas has its own effect on the overall pressure
Dalton’s Law: PT = P1 + P2 + P3….
Courtesy of John Dalton (who also gave us Atomic Theory)

15. WB CHECK:
Which KMT assumption about gases explains Dalton’s Law of partial pressures?

16. POINT > Explain Partial Pressures (Dalton’s Law)
The partial pressure exerted by water vapor is often important in gas collection experiments
The pressure of the gas collected can be determined using Dalton’s Law:
Patm = PH2O + Pgas
The water vapor pressure (PH2O) at a given temp can be found in a Table (R-63 in your textbook)

17. WB CHECK:
What is the water vapor pressure
At 25.0 C (in mmHg)?
23.8 mmHg

18. Homework:
Read pages
Complete FA #1-6 page
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