1. Chapter 11
Gases

2. Conditions that affect gases
volume
pressure
temperature
# of particles

3. Pressure and Force
Pressure = force
area
Example of pressure:

4. Pressure Atmospheric pressure- 14.7 psi
78% nitrogen, 21% oxygen and 1% other gas

5. Pressure Ways to measure pressure: Open end manometer
Closed end manometer
Barometer

6. Pressure

7. Pressure
Barometer-measures atmospheric pressure

8. Pressure Units of Pressure: see pg.364
Millimeters of mercury
Kilopascals,pascals
atmospheres
torr
760 mmHg = 1 atm= kPa = 760 torr

9. Pressure Conversions Examples: Practice: a. Atm b. kPa
Convert the pressure of 775 mm Hg to kPa and to atm.
Practice:
Convert a pressure of 750. torr to
a. Atm
b. kPa

10. Standard Conditions STP- Standard Temperature and Pressure
Agreed upon standard
0°C and 1 atm

11. Dalton’s Law of Partial Pressures
Each individual gas has its own pressure (partial pressure)
Ptotal = Pa + Pb + Pc + …..

12. Sample problems for Dalton’s Law
Example: Calculate the partial pressure in mm Hg exerted by the four main gases in air: nitrogen, oxygen, argon and carbon dioxide. Their abundance by volume is 78.08%, 20.95%, .934% and .035 % respectively.

13. Sample problems for Dalton’s Law
Example : In a sample containing carbon dioxide, nitrogen and oxygen at exactly 1 atm. The partial pressure of CO2 is .285 torr and the partial pressure of N2 is torr. What is the partial pressure of O2?

14. Dalton’s Law of Partial Pressures
Collecting gas over water:
-useful for gases that do not dissolve or react with water
- water has a partial pressure, it increases with increased temp.
-must use a table for the exact value pg. 859
Patm = Pgas + PH20

15. Dalton’s Law of Partial Pressures

16. Sample problems for Dalton’s Law
Example: Oxygen gas was collected from the decomposition of potassium chlorate. The atmospheric pressure was torr and the temperature of the water was 20.0 C. What was the partial pressure of the oxygen gas collected?

17. Sample problems for Dalton’s Law
Practice: A sample of nitrogen gas is collected over water at a temperature of °C. What is the pressure of the nitrogen gas if the atmospheric pressure is 785 mm Hg?

18. The Simple Gas Laws Boyle’s Law Charles’s Law Gay-Lussac’s Law
The Combined Gas Law

19. Boyle’s Law
When temp. and # of particles are constant the pressure and volume of a gas are inversely proportional
P1V1= P2V2

20. Boyle’s Law -practice
Example: A sample of gas has a volume of mL when its pressure is .947 atm. What will the volume of the gas be at a pressure of atm if the pressure and amount of gas remain constant?
Practice: A helium filled balloon contains 125 mL of gas at a pressure of .974 atm What volume will the gas occupy at standard pressure?

21. Charles’s Law
With constant amount of gas and pressure the volume and temperature of a gas will have a directly proportional relationship
V1 = V2
T T2
NOTE: TEMPERATURE MUST BE IN KELVIN
K= ° C + 273

22. Charles's Law Practice
Example: A sample of neon gas occupies a volume of 752 mL at 25 ° C. What volume will the gas occupy at 50° C if the pressure remains constant?
Practice: A balloon filled with oxygen gas occupies a volume of 5.5 L at 25° C. What volume will the gas occupy at 100. ° C?

23. Gay-Lussac’s Law
Pressure and temperature of a gas are directly proportional if the amount and volume of gas remain constant
P1 = P2
T T2

24. Gay-Lussac’s Law Practice
Example: The gas in an aerosol can is at a pressure of 3.00 atm at 25°C. What would the pressure of the gas be if the can was heated to 52° C?
Practice: The temperature within a car tire at the beginning of a long trip is 25° C. At the end of the trip the tire has a pressure of 1.80 atm. What is the final temperature within the tire if its original pressure was 1.75 atm?

25. The Combined Gas Law
Expresses all of the simple gas laws, relating temperature, pressure and volume of a gas as long as the amount of gas remains constant.
P1V1 = P2V2
T1 T2
MEMORIZE this law, cross out the factors that remain constant.

26. The Combined Gas Law Practice
Example:A helium filled balloon has a volume of 50.0L at 25° C and 1.08 atm. What will the new volume be if its pressure is decreased to .855 atm and the temperature decreases to 10. ° C?
Practice: The volume of a gas at 27.0 ° C and .200 atm is 80.0 mL. What volume will the same gas sample occupy at standard conditions?

27. END of MATERIAL FOR TEST 1

28. Measuring and Comparing the Volumes of Reacting Gases
Law of Combining Volumes
at constant temperature and pressure, the volumes of gases react and can be expressed as whole numbers
Try this: Write and balance and equation for each.
hydrogen gas and oxygen gas produces water vapor
hydrogen gas and chlorine gas produce hydrogen chloride gas
Now go to pg.378 and check the results

29. Measuring and Comparing the Volumes of Reacting Gases
Avogadro’s Law
Equal volumes of gases at the same temperature and pressure contain equal # of molecules
standard molar volume of a gas
one mole of any gas at STP = 22.4L of that gas

30. Measuring and Comparing the Volumes of Reacting Gases
Example: at STP
2H2(g) + O2(g)  2H2O(g)
__ L __ L __ L
2 mL 1 mL 2 mL
__ molecules__ molecule __ molecules
__ moles 1 mole __ moles
44.8 L 22.4 L __ L

31. Using Molar Volume of a Gas
You are planning an experiment that requires mol of nitrogen monoxide gas. What volume would you need at STP?
Practice: A chemical reaction produces mol of oxygen gas. What volume in liters is occupied by this gas at STP?

32. Using Molar Volume of a Gas
Challenge: Suppose you need 4.22 g of chlorine gas,Cl2. What volume at STP would you expect to use?

33. Stoichiometry of Gases
- if constant temp and pressure, just use the molar ratio from the equation!!
- volume and moles are the same ratio as the equation!!

34. Stoichiometry of Gases
Example: Propane is C3H8.
Write the combustion reaction for propane.
a. What will be the volume, in liters of oxygen required for the complete combustion of .350 L of propane? Assume STP
b. What will be the volume of carbon dioxide produced in the same reaction starting with .350 L of propane? Assume STP

35. Stoichiometry of Gases
Practice: Xenon gas reacts with fluorine gas to produce the gas xenon hexafluoride. Write the equation for this reaction.
a. Assuming constant temperature and pressure, what volume of xenon should be used to make 3.14 L of XeF6?
b. What volume of fluorine gas should be used to create 3.14 L of XeF6?

36. The Ideal Gas Law
includes, temperature, pressure, volume and # of moles
single conditions, not P1,P2
PV= nRT

37. PV=nRT P= pressure (must match unit of pressure in R value)
V= volume (must be in L)
N= # of moles (convert to moles if given grams)
T= temperature (Kelvin)
R= ideal gas law constant
R= L . atm
mol.K
See various numerical values for R on pg. 384

38. Ideal Gas Law Practice
Example: What is the pressure in atm exerted by a .500 mol sample of nitrogen gas in a 10.0L container at 298K?
Practice: A 2.07 L cylinder contains 2.88 mol of helium gas at 22° C. What is the pressure in atm of the gas in the cylinder? (P= 33.7 atm)

39. Ideal Gas Law Practice
Practice: A tank of hydrogen gas has a volume of 22.9 L and holds 14.0 mol of the gas at 12° C. What is the reading on the pressure gauge in mm Hg?(14.3 atm1.09X104 mmHg)
Practice: A reaction yields mol of oxygen gas. What volume in mL will the gas occupy if it is collected at 43 °C and .926 atm? (.240 L240. mL)

40. Effusion and diffusion
lighter molecules move faster
Graham’s Law of Effusion-the rate of effusion and diffusion is inversely proportional to the square root of the molecular weights of the gases

41. Graham’s Law Practice
Example: Nitrogen gas effuses through a pinhole 1.7 times as fast as another element under the same conditions. Estimate the other element’s mass and determine its probable identity.

42. Graham’s Law Practice
Practice: Compare the rates of effusion of hydrogen and oxygen gas at the same conditions. (Remember, both are diatomic.)