1. Gases

2. Gases
I. Physical Properties

3. A. Characteristics of Gases
expand to fill any container
fluids (like liquids)
have very low densities

4. A. Characteristics of Gases
can be compressed
undergo diffusion & effusion

5. K = ºC + 273 B. Temperature always use KELVIN when working with gasesºF ºC K
-459 32
212
-273
100
273
373
K = ºC + 273

6. C. Pressure
Which shoes create the most pressure?

7. C. Pressure barometer measures atmospheric pressure Aneroid Barometer
Mercury Barometer
Aneroid Barometer

8. C. Pressure manometer measures contained gas pressure U-tube Manometer
Bourdon-tube gauge

9. C. Pressure KEY UNITS AT SEA LEVEL 101.325 kPa (kilopascal) 1 atm
760 mm Hg
760 torr
14.7 psi

10. Standard Temperature & Pressure
D. STP
STP
Standard Temperature & Pressure
0°C K
1 atm kPa
-OR-

11. Gases
II. The Gas Laws P V T

12. P1V1 = P2V2 A. Boyle’s Law inverse relation!
example: car engine cylinder breathing
inverse relation! P V

13. A. Boyle’s Law

14. proportional relation!
B. Charles’ Law
example: hot air balloons
V1 = V2 T1 T2
proportional relation! V T

15. B. Charles’ Law

16. proportional relation!
C. Gay-Lussac’s Law
example: autoclave (sterlization)
P1 = P2 T1 T2
proportional relation! P T

17. D. Combined Gas Law
P1V1 T1 =
P2V2 T2
P1V1T2 = P2V2T1

19. E. Gas Law Problem #1
A gas occupies 473 cm3 at 36°C. Find its volume at 94°C.

20. E. Gas Law Problem #2
A gas occupies 100. mL at kPa. Find its volume at 200. kPa.

21. E. Gas Law Problem #3
A gas occupies 7.84 cm3 at 71.8 kPa & 25°C. Find its volume at STP.

22. E. Gas Law Problem #4
A gas’ pressure is 765 torr at 23°C. At what temperature will the pressure be 560. torr?

23. Gases
Ideal Gas Law

24. Avogadro’s Principle
CO2 Ne
Equal volumes of gases contain equal numbers of moles
at constant temp & pressure
true for any gas V n

25. UNIVERSAL GAS CONSTANT
Ideal Gas Law
PV=nRT
UNIVERSAL GAS CONSTANT
R= Latm/molK

26. Ideal Gas Law Problem #5
Calculate the pressure in atmospheres of mol of He at 16°C & occupying L.

27. Ideal Gas Law Problem #6
Find the volume of 85 g of O2 at 25°C and kPa.

28. Gas Stoichiometry at Non-STP Conditions
Gases
Gas Stoichiometry at Non-STP Conditions

29. Gas Stoichiometry at STP: moles  liters of a gas: use 22.4 L = 1 mol
How many moles are in a 4.5 L helium balloon at STP?

30. Gas Stoichiometry at STP: moles  liters of a gas: use 22.4 L = 1 mol
__H2 + __O2  __H2O
How many grams of water can be formed if you start with 2.3 L of H2?

31. Gas Stoichiometry at non-STP given liters of gas?
start with ideal gas law
looking for liters of gas?
start with stoichiometry conv.

32. Gas Stoichiometry Problem
What volume of CO2 forms from the decomposition of 5.25 g of CaCO3 at 103 kPa & 25ºC?
CaCO3  CaO CO2

33. Gas Stoichiometry Problem
What volume of CO2 forms from g of CaCO3 at 103 kPa & 25ºC?

34. Gas Stoichiometry Problem
How many grams of Al2O3 are formed from L of O2 at 97.3 kPa & 21°C?
4 Al O2  2 Al2O3

35. Gas Stoichiometry Problem
How many grams of Al2O3 are formed from 15.0 L of O2 at 97.3 kPa & 21°C?
4 Al O2  2 Al2O3

36. Gases
Two More Laws

37. Ptotal = P1 + P2 + ... Dalton’s Law
The total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases.
Ptotal = P1 + P
When H2 gas is collected by water displacement, the gas in the collection bottle is actually a mixture of H2 and water vapor.

38. Dalton’s Law
Hydrogen gas is collected over water at 22.5°C. Find the pressure of the dry gas if the atmospheric pressure is 94.4 kPa.

39. Dalton’s Law
A gas is collected over water at a temp of 35.0°C when the barometric pressure is torr. What is the partial pressure of the dry gas?

40. Graham’s Law diffusion
spreading of gas molecules throughout a container until evenly distributed
effusion
passing of gas molecules through a tiny opening in a container

41. Graham’s Law speed of diffusion/effusion
KE is determined by temp of gas
at same temp & KE, heavier molecules move more slowly

42. Graham’s Law Graham’s Law
rate of diffusion of a gas is inversely related to square root of molar mass

43. Graham’s Law
Determine the relative rate of diffusion for krypton and bromine.

44. Graham’s Law
A molecule of oxygen gas has an average speed of 12.3 m/s at a given temp and pressure. What is the average speed of hydrogen molecules at the same conditions?

45. Graham’s Law
An unknown gas diffuses 4.0 times faster than O2. Find its molar mass.