TEMA PARA LA MATERIA DE QUÍMICA...t/t

1. Gases: Behavior and
Calculations
QBA Miguel A. Castro Ramírez

2. Make two lists of equal size.
• What I know about • What I know about
gases from chemistry gases from outside of
class chemistry class

3. Compare contrast a
basketball shot with an over-
inflated ball and a flat ball.

4. What would happen if your
airbag was filled with liquid
instead? Solid?

5. Changes in a Gas
• What factor explains
why SCUBA divers
can carry all the
oxygen they need in a
small tank?

6. Review Questions
1. What is pressure?
2. How are the atoms/molecules in a gas
arranged (compared to a liquid/solid)?
3. Define temperature.

7. Pressure
• Pressure = force per
unit area

8. Gases and Kinetic Theory
• Molecules in constant, rapid, random
motion
• No forces exist between molecules
• Temperature is a measure of
molecular kinetic energy.
• More molecules colliding with the
container = more pressure

9. What affects pressure?
1.
2.
3.

10. Variables
P (pressure) measures in kilopascals (kPa)
V (volume) measured in liters (L)
T (temperature) measured in Kelvins (K)
n (number of moles)

11. Kelvin Scale
• Temperature in oC
+ 273
= Temperature in K
• NOT DEGREES K!

12. Kelvin Scale • 60oC = ?
• 28oC = ?
• -6oC = ?
• 310 K = ?
• 271 K = ?

13. Animated Gas Lab
• http://intro.chem.okstate.edu/1314F00/Laboratory

14. Mathematical Relationships
• Inverse Relationship:
– One value goes down while the other goes up
• Direct Relationship:
– Both values change in the same direction

15. Boyle’s Law
• If the volume of gas is
lowered, how is the
pressure affected?
(Temperature held
constant.)
• http://www.grc.nasa.gov/WWW/

16. Boyle’s Law
• Pressure and volume
share an inverse
relationship, thus…
P1V1 = P2V2

17. Boyle’s Law
• Nitrous oxide (N2O) is used as an anesthetic. The
pressure on 2.50 L of N2O changes from 105 kPa to
40.5 kPa. If the temperature does not change, what will
the new volume be?

18. Boyle’s Law
• Carbon dioxide gas is contained within a balloon at a
pressure of 160 kPa. If the balloon’s volume is
suddenly decreased from 0.50 L to 0.20 L, will the
pressure increase or decrease? What will the new
pressure be? (Temperature remains constant.)

19. Boyle’s Law
• You have volunteered to decorate the gym with helium
balloons for a party. You find a store that will rent a 25-
L helium tank filled with helium gas at a pressure of
3,040 kPa. You need to fill all 750 balloons with 1 liter
of helium at a pressure of 106 kPa. Will one tank be
enough to fill all the balloons?

20. Boyle’s Law
• The pressure on 2.50 L of anesthetic gas
changes from 105 kPa to 40.5 kPa. What
will be the new volume if the temperature
remains constant?

21. Charles’ Law
• If the temperature of
a gas is lowered,
how is the volume
affected? (Pressure
held constant.)

22. Charles’ Law
• Volume and
temperature share a
direct relationship,
thus…
V1 V2
---- = ----
T1 T2

23. Charles’ Law
• Exactly 5.00 L of air at 50.0oC is warmed to 100.0oC.
What is the new volume if the pressure remains
constant?

24. Charles’ Law
• A SCUBA diver has a 1.50 L tank at a temperature of
25oC. In order to maintain the same pressure, what
temperature would a 1.35 L tank need to be stored at?

25. Charles’ Law
• On a cool morning, (10.0oC), a group of hot air
balloonists fill their balloons with air. They fill their
balloon to ¾ the volume, (1,275,000 L). At what
temperature Celsius will the balloon completely fill with
air (1,700,000 L) if the pressure and amount of gas
remain constant?

26. Charles’ Law
• If a sample of gas occupies 6.80 L at
325oC, what will be its volume at 25oC if the
pressure does not change?

27. Gay-Lussac’s Law
• If the temperature of
a gas is lowered,
what happens to the
pressure? (Volume is
held constant.)

28. Gay-Lussac’s Law
• Pressure and
temperature share a
direct relationship,
thus…
P1 P2
---- = ----
T1 T2

29. Gay-Lussac’s Law
• Aerosol cans carry warning labels that say not to
incinerate (burn) them or store them above a certain
temperature. Why? The gas used in an aerosol can is
at a pressure of 103 kPa at 25oC. If the can is thrown in
a fire and the temperature reaches 928oC, what will the
new pressure be?

30. Which Law?
• A plastic container of nitrogen is placed into
a freezer. If the volume of the container is
1.50 L at 20oC, what will the volume be
after the temperature drops to –2oC?

31. Which Law?
• A sample of neon has a pressure of 16.8 kPa at
489 K. If the volume does not change, what will
the pressure be at 210 K?

32. Which Law?
• If the pressure of a 5.0 L of a gas changes
from 125 kPa to 700 kPa, what happens to
the volume?
• A sample of hydrogen gas has a volume of
56.0 L at 25oC. If the volume rises to 65.0
L, at what temperature is the gas now?

33. Which Law?
• A sample of hydrogen gas has a volume of
56.0 L at 25oC. If the volume rises to 65.0
L, at what temperature is the gas now?

34. Gas Laws
• Boyle’s Law: PRESSURE and VOLUME are
inversely proportional
• Charles’ Law: VOLUME and TEMPERATURE
are directly proportional
• Guy-Lussac’s Law: PRESSURE and
TEMPERATURE are directly proportional

35. Combined Gas Law
• Can be used if none of
the three variables (P, V,
and T) remain constant.
P1V1 P2V2
-------- = --------
T1 T2

36. Combined Gas Law
• A 2.50 liter balloon is filled with argon. The
balloon has a pressure of 118 kPa at room
temperature, 25oC. If the balloon is put into
a freezer (temperature of -6oC) and its
volume drops to 2.35 L, what is its new
pressure?

37. Combined Gas Law
• The volume of a gas-filled balloon is 30.0 L
at 313 K and 153 kPa. What would the
volume be at standard temperature and
pressure?

38. Combined Gas Law
• If the temperature and pressure of 4.0 liters
of argon gas are changed from 65°C to
85°C and 150 kPa to 91 kPa respectively,
calculate the change in the volume of the
gas.

39. Use The Combined Gas Law…
• On a warm May day (80oF or 27oC), a scuba
diver on a boat takes 18.0 liters of air from
a storage tank (stored at a relatively low
pressure of 140 kPa) and transfers it to a
small (7-liter) tank. When he jumps into the
water, the pressure gauge on the tank
reads 341 kPa. What temperature is the
ocean?

40. Challenge Problem
• Examine the following web page.
Determine the pressure that the helium in a
large tank is stored at if the tank is at room
temperature and is 4 feet tall and eleven
inches wide.
http://www.arneswarehouse.com/heliumtank.htm

41. Ideal Gases

42. • Besides volume,
temperature, and
pressure… what can
we change about the
gas in the balloon?

43. Moles of a Gas
• 1.0 moles of a gas (at STP) takes
up 22.4 L.
• How does increasing the number
of moles affect the volume of gas?
• Direct or inverse relationship?

44. Moles of a Gas
• Moles / Volume is directly proportional.
• Moles (n) can now be added to the
combined gas law!

45. Calculate the CONSTANT @ STP
P=
T=
V=
n=

46. CONSTANT (R)
8.3 L x kPa / K x mol

47. Ideal Gas Law
• Contains pressure, volume, moles,
temperature (in K) and the constant that
relates the 4 quantities.
PxV
n = ---------- or PV = nRT
RxT

48. Example 1
• A deep underground cavern contains 2240
liters of space filled with methane gas, CH4.
The gas is at a pressure of 150 kPa and a
temperature of 40oC. How many moles of
CH4 does the cavern contain?

49. Example 1, part 2
• How many grams of CH4 does the cavern
contain?

50. Real Gases
• Do not conform exactly to the ratio PV = nRT
• (Very close around “normal” temperatures and
pressures.)
• Real gases differ most from an ideal gas at low
temperatures and high pressures… WHY?

51. Real Gases
• What happens to a gas at an
extremely low temperature?
• What happens to gases at
extremely high pressures?

52. Example 2
• What is the volume occupied by 0.900 mol
of C2H2 at STP?

53. Example 3
• How large would a container have to be to
hold 3000 g of propane gas (C3H8) if the gas
was stored at 25oC and a pressure of 500
kPa?

54. Example 4
• A 50.00 liter tank at -15°C
contains 14.00 grams of
helium gas. How many
moles of gas are in the
tank?
• At what pressure is the gas
within the tank?

55. Examples 5 and 6
• Determine the number of • At what
moles of Krypton temperature will
contained in a 3.25 liter 0.654 moles of
gas tank at 540 kPa and neon gas
28°C. If the gas is
Oxygen instead of occupy 12.30
Krypton, will the answer liters at 195
be the same? Why or kPa?
why not?

56. Fill in using Ideal Gas Law.
Gas Argon Nitrogen Krypton
Pressure 0.96 kPa --- 252 kPa
Volume --- 5.25 L 465 L
Temperature 200oC 373 K ---
Moles --- 0.0857 mol 25.0 mol
Mass 12.5 g --- ---

57. Density
• Calculate the density (g/m3) of the following
gases at standard temperature and
pressure:
• Hydrogen, Oxygen, Chlorine, Radon
• 1 liter = 0.001 cubic meters (m3)