1. Objectives
To learn about atmospheric pressure and how barometers work
To learn the units of pressure
To understand how the pressure and volume of a gas are related
To do calculations involving Boyle’s Law
To learn about absolute zero
To understand how the volume and temperature of a gas are related
To do calculations involving Charles’s Law
To understand how the volume and number of moles of a gas are related
To do calculations involving Avogadro’s Law

2. A. Pressure
Measuring Pressure
Barometer – device that measures atmospheric pressure
Invented by Evangelista Torricelli in 1643

3. A. Pressure
Atmospheric Pressure
Changing weather conditions

4. A. Pressure
Atmospheric Pressure
Changing altitude

5. A. Pressure
Units of Pressure
1 standard atmosphere
= atm
= mm Hg
= torr
= 101,325 Pa

6. A. Pressure
Units of Pressure
A manometer measures the pressure of a gas in a container.

7. B. Pressure and Volume: Boyle’s Law
Robert Boyle’s experiment

8. B. Pressure and Volume: Boyle’s Law

9. B. Pressure and Volume: Boyle’s Law
Graphing Boyle’s results

10. B. Pressure and Volume: Boyle’s Law
This graph has the shape of half of a hyperbola with an equation PV = k
Volume and pressure are inversely proportional.
If one increases the other decreases.

11. B. Pressure and Volume: Boyle’s Law
Another way of stating Boyle’s Law is
P1V1 = P2V2
(constant temperature and amount of gas)

12. C. Volume and Temperature: Charles’s Law
Graphing data for several gases

13. C. Volume and Temperature: Charles’s Law
It is easier to write an equation for the relationship if the lines intersect the origin of the graph.
Use absolute zero for the temperature

14. C. Volume and Temperature: Charles’s Law
These graphs are lines with an equation V = bT (where T is in kelvins)
Volume and temperature are directly proportional.
If one increases the other increases.
Another way of stating Charles’s Law is V1 = V2
T T2
(constant pressure and amount of gas)

15. D. Volume and Moles: Avogadro’s Law

16. D. Volume and Moles: Avogadro’s Law
Volume and moles are directly proportional.
If one increases the other increases.
V = an
constant temperature and pressure
Another way of stating Avogadro’s Law is V1 = V2
n n2
(constant temperature and pressure)

17. Objectives
To understand the ideal gas law and use it in calculations
To understand the relationship between the partial and total pressure of a gas mixture
To do calculations involving Dalton’s law of partial pressures
To understand the molar volume of an ideal gas
To learn the definition of STP
To do stoichiometry calculations using the ideal gas law

18. A. The Ideal Gas Law
Boyle’s Law V = k (at constant T and n) P
Charles’s Law V = bT (at constant P and n)
Avogadro’s Law V = an (at constant T and P)
We can combine these equations to get

19. A. The Ideal Gas Law
Rearranging the equation gives the ideal gas law
PV = nRT
R = L atm
mol K

20. B. Dalton’s Law of Partial Pressures
What happens to the pressure of a gas as we mix different gases in the container?

21. B. Dalton’s Law of Partial Pressures
For a mixtures of gases in a container, the total pressure exerted is the sum of the partial pressures of the gases present.
Ptotal = P1 + P2 + P3

22. B. Dalton’s Law of Partial Pressures
The pressure of the gas is affected by the number of particles.
The pressure is independent of the nature of the particles.

23. B. Dalton’s Law of Partial Pressures
Two crucial things we learn from this are:
The volume of the individual particles is not very important.
The forces among the particles must not be very important.

24. B. Dalton’s Law of Partial Pressures
Collecting a gas over water
Total pressure is the pressure of the gas + the vapor pressure of the water.

25. B. Dalton’s Law of Partial Pressures
Collecting a gas over water
How can we find the pressure of the gas collected alone?

26. C. Gas Stoichiometry
Molar Volume
Standard temperature and pressure (STP)
0oC and 1 atm
For one mole of a gas at STP
Molar volume of an ideal gas at STP L

27. Objectives
To understand the relationship between laws and models (theories)
To understand the postulates of the kinetic molecular theory
To understand temperature
To learn how the kinetic molecular theory explains the gas laws
To describe the properties of real gases

28. A. Laws and Models: A Review

29. A. Laws and Models: A Review
A model can never be proved absolutely true.
A model is an approximation and is destined to be modified.

30. B. The Kinetic Molecular Theory of Gases

31. C. The Implications of the Kinetic Molecular Theory
Meaning of temperature – Kelvin temperature is directly proportional to the average kinetic energy of the gas particles
Relationship between Pressure and Temperature – gas pressure increases as the temperature increases because the particles speed up
Relationship between Volume and Temperature – volume of a gas increases with temperature because the particles speed up

32. D. Real Gases
Gases do not behave ideally under conditions of high pressure and low temperature.
Why?

33. D. Real Gases
At high pressure the volume is decreased
Molecule volumes become important
Attractions become important