1. Sit down and get ready for the test, I will hand them out when the bell rings. You have until 8:10
DMA 3/21/11

2. You can have a few minutes to finish your test, if you are already done, work on something quietly
DMA 3/21/11

3. When you are done with your test, begin the following:
In your book, read (it is important that you actually read this) Ch 13-1 (pg ) and take notes which include the following info:
The 6 physical properties that are common to all gases
What it means when the terms “atom” “diatomic molecule” or “polyatomic molecule” are used when taking about gases
The 6 postulates of the Kinetic-molecular theory of gases
Answer question #5 on pg. 423
This is homework if you don’t get it done today

4. Name 4 physical properties of gases
DMA 3/22/11
Name 4 physical properties of gases

5. The Nature of Gases-physical properties
Gases expand to fill their containers
Gases are fluid – they flow
Gases have low density
1/1000 the density of the equivalent liquid or solid
Gases are compressible
Gases effuse and diffuse

6. Kinetic Molecular Theory
Gases are made of particles, which have mass
Particles of matter are ALWAYS in motion
Volume of individual particles is  zero.
Collisions of particles with container walls cause pressure exerted by gas.
Particles exert no forces on each other.
Average kinetic energy proportional to temperature in Kelvin of a gas.

7. Measuring Gases
When you are measuring a gas, you want to know four things about it:
1. n --Amount of the gas-this means in moles represented by the letter n
2. V—volume
3. T—temperature
4. P—pressure

8. Temperature When using the gas laws, temperature is measured in Kelvin
To find Kelvin:
Add 273 to Celcius.
T(K)=T(oC) + 273

9. Converting Celsius to Kelvin
Gas law problems involving temperature require
that the temperature be in KELVINS!
Kelvins = C + 273
°C = Kelvins - 273

10. Celcius & Kelvin Temperature Scales

11. Converting Temperature
Convert the following temperatures to the Kelvin scale.
20 C
85 C
–15 C
–190 C

12. An Early Barometer Mercury Barometer
Atmospheric pressure– the pressure
exerted by the air in the atmosphere.
Barometer-measures air pressure
The normal pressure due to
the atmosphere at sea level
can support a column of
mercury that is 760 mm high.

13. Which shoes create the most pressure?

14. Standard Temperature and Pressure “STP”
P = 1 atmosphere (760 torr)
T = 0°C (273 Kelvins)
The molar volume of an ideal gas is liters at STP

15. Pressure
Is caused by the collisions of molecules with the walls of a container
is equal to force/unit area
SI units = Newton/meter2 = 1 Pascal (Pa)
1 standard atmosphere = 101,325 Pa= kPa
1 standard atmosphere = 1 atm =
760 mm Hg = 760 torr

16. Converting Pressure Units
Change 5 atmospheres (atm) into millimeters mercury (mm Hg).
1 atm = 760 mm Hg
5 atm x 760 mm Hg =
1 atm
3800 mm Hg

17. Converting Pressure Units
Change 1900 mm mercury (mm Hg) into atmospheres (atm).
1 atm = 760 mm Hg
1900 mm Hg x 1 atm =
760 mm Hg
2.5 atm

18. Converting Pressure Units
Change 560 kilopascals into millimeters mercury (mm Hg).
101.3 kPa = 760 mm Hg
560 kPa x 760 mm Hg =
101.3 kPa
4201 mm Hg

19. Converting Pressure Units
Change 1013 kilopascals into millimeters mercury (mm Hg).
1 atm = kPa
1013 atm x 1 atm =
101.3 kPa
10 atm

20. Boyle’s Law* Pressure is inversely proportional to volume
when temperature is held constant.
Pressure ´ Volume = Constant
P1V1 = P2V2 (T = constant)

21. If pressure increases then volume decreases.
A Graph of Boyle’s Law
If pressure increases then volume decreases.
If pressure decreases, then volume increases.
Inversely proportional.

22. Charles’s Law
The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin. (P = constant)

23. Practice Problem P1 = 710 mm Hg, V1 = 2.40 L, P2 = 75 mm Hg V2 = ?
A gas at constant temperature occupies a volume of 2.40 L and exerts a pressure of 710 mm Hg What volume will the gas occupy at a pressure of 75 mm Hg?
P1 = 710 mm Hg, V1 = 2.40 L, P2 = 75 mm Hg
V2 = ?
P1V1 = P2V2 (Boyle’s Law)
710 mm Hg x 2.40 L = 75 mm Hg x V2
V2 = 22.7 L
The new volume will be 22.7 liters.

24. Practice Problem P1 = 3.4 atm, V1 = 14 L, P2 = 5 atm V2 = ?
Sulfur dioxide gas at a pressure of 3.4 atm and a volume of 14 liters increases pressure to 5 atm. What is the resulting volume?
P1 = 3.4 atm, V1 = 14 L, P2 = 5 atm
V2 = ?
P1V1 = P2V2 (Boyle’s Law)
3.4 atm x 14 L = 5 atm x V2
V2 = 9.5 L
The new volume will be 9.5 liters.

25. Practice Problem P1 = 11.8 kPa, V1 = 420 ml, V2 = 630 ml P2 = ?
Carbon monoxide at a pressure of kPa in a vessel of 420 ml expands to a new volume of 630 ml. What is the new pressure in kPa?
P1 = 11.8 kPa, V1 = 420 ml, V2 = 630 ml
P2 = ?
P1V1 = P2V2 (Boyle’s Law)
11.8 kPa x 420 ml = P2 x 630 ml
P2 = 7.9 kPa
The new pressure is 7.9 kilopascals.

26. Practice Problem
Given 90 ml of H2 gas collected when the temperature is 27 C, how many ml will H2 occupy at 42 C?
V1 = 90 ml, T1 = 27 C, T2 = 42 C, V2 = ?
T1 = 27 C = 300 K
T2 = 42 C = 315 K
V1 = V2 (Charles’ Law)
T1 T2
90 ml = V2 V2 = 90 ml x 315 K
300 K K K
V2 = 94.5 ml

27. Why Don’t I Get a Constant Value for PV = k?
Air is not made
of ideal gases
2. Real gases
deviate from
ideal behavior
at high pressure

28. What you need to do

29. DMA
Using the conversions you have in your notes, convert the following pressure units:
20 mm Hg = ? atm
3 atm = ? kPa
3 atm = ? mm Hg
500 mm Hg = ? kPa
200 kPa = ? atm

30. DMA
What is the kinetic molecular theory?

31. Gay Lussac’s Law The pressure and temperature of a gas are
directly related, provided that the volume
remains constant.

32. The Combined Gas Law The combined gas law expresses the relationship
between pressure, volume and temperature of a
fixed amount of gas.
Why would you need this law when you already have all the others? What is different here?

33. Combined Gas Law
If you should only need one of the other gas laws, you can cover up the item that is constant and you will get that gas law! = P1 V1 P2
Boyle’s Law
Charles’ Law
Gay-Lussac’s Law V2 T1 T2

34. Combined Gas Law Problem
A sample of helium gas has a volume of L, a pressure of atm and a temperature of 29°C. What is the new temperature(°C) of the gas at a volume of mL and a pressure of 3.20atm?
What do you need to do first?
Set up Data Table
P1 = atm V1 = 180 mL T1 = 302 K
P2 = atm V2= 90 mL T2 = ??

35. Calculation = 604 K P1 = 0.800 atm V1 = 180 mL T1 = 302 K
P1 V P2 V2
= P1 V1 T2 = P2 V2 T1
T T2
T2 = P2 V2 T1
P1 V1
T2 = 3.20 atm x mL x 302 K atm x mL
T2 = 604 K = °C
= K

36. Learning Check
A gas has a volume of 675 mL at 35°C and atm pressure. What is the temperature in °C when the gas has a volume of L and a pressure of 802 mm Hg?

37. One More Practice Problem
A balloon has a volume of 785 mL on a fall day when the temperature is 21°C. In the winter, the gas cools to 0°C. What is the new volume of the balloon?

38. To Do Today Finish Boyle’s Law and Charles’ Law homework-due today!
Combined gas law practice problems-due Monday
In book-review Ch 13 to help your understanding 

39. DMA 3/28/11
A balloon has a volume of 785 mL on a fall day when the temperature is 21°C. In the winter, the gas cools to 0°C. What is the new volume of the balloon?

40. Dalton’s Law
John Dalton

41. Dalton’s Law of Partial Pressures
For a mixture of gases in a container,
PTotal = P1 + P2 + P
This is particularly useful in calculating the pressure of gases collected over water.

42. Dalton’s Law of Partial Pressures
2 H2O2 (l) ---> 2 H2O (g) + O2 (g)
0.32 atm atm
What is the total pressure in the flask?
Ptotal in gas mixture = PA + PB + ...
Therefore,
Ptotal = PH2O + PO2 = atm
Dalton’s Law: total P is sum of PARTIAL pressures.

43. Avogadro’s Hypothesis
Equal volumes of gases at the same T and P have the same number of molecules.
V = n (RT/P) = kn
V and n are directly related.
twice as many molecules

44. Avogadro’s Hypothesis and Kinetic Molecular Theory
The gases in this experiment are all measured at the same T and V.
P proportional to n

45. P V = n R T IDEAL GAS LAW Brings together gas properties.
Can be derived from experiment and theory.
BE SURE YOU KNOW THIS EQUATION!

46. Using PV = nRT L • atm Mol • K
P = Pressure
V = Volume
T = Temperature R =
n = number of moles
R is a constant, called the Ideal Gas Constant
Instead of learning a different value for R for all the possible unit combinations, we can just memorize one value and convert the units to match R.
L • atm
Mol • K

47. Using PV = nRT
How much N2 is required to fill a small room with a volume of 960 cubic feet (27,000 L) to 745 mm Hg at 25 oC?
Solution
1. Get all data into proper units
V = 27,000 L
T = 25 oC = 298 K
P = 745 mm Hg (1 atm/760 mm Hg) = 0.98 atm
And we always know R, L atm / mol K

48. Using PV = nRT 2. Now plug in those values and solve for the unknown.
How much N2 is req’d to fill a small room with a volume of 960 cubic feet (27,000 L) to P = 745 mm Hg at 25 oC?
Solution
2. Now plug in those values and solve for the unknown.
PV = nRT
RT RT
n = 1.1 x 103 mol (or about 30 kg of gas)

49. Learning Check
Dinitrogen monoxide (N2O), laughing gas, is used by dentists as an anesthetic. If mol of gas occupies a 20.0 L tank at 23°C, what is the pressure (mm Hg) in the tank in the dentist office?

50. Try This One
A sample of neon gas used in a neon sign has a volume of 15 L at STP. What is the volume (L) of the neon gas at 2.0 atm and –25°C?

51. DMA 3/29/11
A sample of neon gas used in a neon sign has a volume of 15 L at STP. What is the volume (L) of the neon gas at 2.0 atm and –25°C?
The first thing you need to do is decide which law to use!

53. At STP For example What is the volume at STP of 4.00 g of CH4?
At STP determining the amount of gas required or produced is easy.
22.4 L = 1 mole
For example
What is the volume at STP of 4.00 g of CH4?
How many grams of He are present in 8.0 L of gas at STP?

54. Gas Stoichiometry: Practice!
How many liters of O2 at STP are required to produce 20.3 g of H2O?

55. Gases and Stoichiometry
2 H2O2 (l) ---> 2 H2O (g) + O2 (g)
Decompose 1.1 g of H2O2 in a flask with a volume of 2.50 L. What is the volume of O2 at STP?
Bombardier beetle uses decomposition of hydrogen peroxide to defend itself.

56. Gases and Stoichiometry
2 H2O2 (l) ---> 2 H2O (g) + O2 (g)
Decompose 1.1 g of H2O2 in a flask with a volume of 2.50 L. What is the volume of O2 at STP?
Solution
1.1 g H2O mol H2O mol O L O2
34 g H2O mol H2O mol O2
= 0.36 L O2 at STP

57. Not At STP Chemical reactions happen in MOLES.
If you know how much gas - change it to moles
Use the Ideal Gas Law n = PV/RT
If you want to find how much gas - use moles to figure out volume V = nRT/P

58. Example #1 HCl(g) can be formed by the following reaction
2NaCl(aq) + H2SO4 (aq)2HCl(g) + Na2SO4(aq)
What mass of NaCl is needed to produce 340 mL of HCl at 1.51 atm at 20ºC?

59. Example #2 2NaCl(aq) + H2SO4 (aq) 2HCl(g) + Na2SO4 (aq)
What volume of HCl gas at 25ºC and 715 mm Hg will be generated if 10.2 g of NaCl react?

60. GAS DIFFUSION AND EFFUSION
diffusion is the gradual mixing of molecules of different gases.
effusion is the movement of molecules through a small hole into an empty container.

61. Diffusion
Diffusion: describes the mixing of gases. The rate of diffusion is the rate of gas mixing.

62. Effusion
Effusion: describes the passage of gas into an evacuated chamber.