Behavior of Gases, Kinetic.pptBehavior of Gases, Kinetic.ppt

Behavior of Gases, Kinetic.ppt

1. BEHAVIOR OF GASES

2. Three States of MatterThree States of Matter

3. _____1. Particles are very close to each other and move in a
fixed position.
_____2. Particles are far apart and move freely.
_____3. Particles are able to vibrate about their fixed
position. Thus, attractions between them are very strong.
_____4. The random motion of the particles and their
freedom to slide against each other result in weaker forces of
attraction. It assumes the shape of the containers. However,
the volume is definite.
_____5. Particles have very weak forces of attraction
between them and account for their unique properties.

4. Physical Characteristics of Gases
Physical Characteristics Typical Units
Volume, V liters (L)
Pressure, P atmosphere
(1 atm = 1.015x10
5
N/m
2
)
Temperature, T Kelvin (K)
Number of atoms or
molecules, n
mole (1 mol = 6.022x10
23

atoms or molecules)

5. Properties of GasesProperties of Gases
•No definable No definable shape or volumeshape or volume
•LowLow mass, with a lot of “free” mass, with a lot of “free”
space (leads to space (leads to lowlow density) density)
•
Can be expanded Can be expanded infinitelyinfinitely and and
placedplaced into a container if force is into a container if force is
exerted.exerted.
•Occupy containers Occupy containers uniformly uniformly
and completelyand completely..
•Escape Escape readilyreadily from containers, from containers,
mix mix rapidlyrapidly..

6. PROPERTIES OF A GAS
•Factors Affecting Gas Pressure
•Amount of Gas
•Increase amount, increase pressure
•Volume
•Reduce volume, increase pressure
•Temperature
•Increase temperature, increase pressure
•Relationship between pressure,
temperature, and volume is explained
through the Gas Laws

7. 7
Gases (Vapors)
Gases expand to fill any
container.
Therefore, gases are highly
compressible.

8. KINETIC MOLECULAR THEORY
(KMT)
Definition:Definition:
Theory used to explain gas laws. Theory used to explain gas laws.
Treats gases as a Treats gases as a collection of particles collection of particles
in rapid, random motionin rapid, random motion..
Applies to Applies to ALLALL gases, regardless of gases, regardless of
chemical identitychemical identity..

9. Molecular ModelMolecular Model
•
Gas molecules are relatively far apart (mostly Gas molecules are relatively far apart (mostly empty empty
space).space).
•
Gas molecules are in Gas molecules are in continuous, rapid, random motion.continuous, rapid, random motion.
•
All collisions between gas molecules are All collisions between gas molecules are elasticelastic (no (no
energy lost or gained in a collision).energy lost or gained in a collision).
•
Gas pressure is caused by Gas pressure is caused by collisionscollisions of molecules with of molecules with
the walls of the container.the walls of the container.
•
Average Temperature of a gas sample is related to its Average Temperature of a gas sample is related to its
kinetic energykinetic energy..

10. 10
Kinetic Molecular Theory (of an Ideal Gas):
1. Gases are composed of molecules or atoms whose size
is negligible compared to the average distance between
them. (Most of the space in the gas container is empty.)
2. Gas molecules move randomly in straight lines in all
directions at various speeds.
3. The forces of attraction or repulsion between gas
molecules are very weak or negligible (except during
collisions)
4. Collisions between gas molecules are considered elastic.
5. The average kinetic energy of a molecule is proportional to
the absolute temperature.

11. 11
molecules of air
1
2
3
Where is the pressure the greatest?
We live in “sea of air”
Why does a diver get the bends?

12. 12

13. 4 VARIABLES THAT CAN BE
ALTERED IN A GAS:
1. AMOUNT OF A GAS
2. VOLUME OF A GAS
3. TEMPERATURE OF A GAS
4. PRESSURE OF A GAS

14. 14
We can measure gases in 4
ways:
Measurement Unit
Amount of gas (n)Moles
Volume (V) Liters (L)
Temperature (T)K
Pressure (P) atm, kPa,
Torr, mm Hg,

15. 1. Amount of Gas
•When we inflate a balloon, we are
adding gas molecules.
•Increasing the number of gas
particles increases the number of
collisions
•thus, the pressure increases
•If temp. is constant- doubling the number
of particles doubles pressure

16. Pressure and the number of
molecules are directly related
•More molecules means more collisions.
•Fewer molecules means fewer
collisions.
•Gases naturally move from areas of high
pressure to low pressure because there
is empty space to move in too- spray
can is example.

17. 17
Common use?
•Aerosol (spray) cans
•gas moves from higher
pressure to lower pressure
•a propellant forces the product
out
•whipped cream, hair spray,
paint.

18. 2. Volume of Gas
•In a smaller container, molecules
have less room to move.
•Hit the sides of the container more
often.
•As volume decreases, pressure
increases. (think of a syringe)

19. 3. Temperature of Gas
•Raising the temperature of a gas
increases the pressure, if the
volume is held constant.
•The molecules hit the walls harder,
and more frequently!
•The only way to increase the volume
at constant pressure is to increase
the temperature.

20. 20
Pressure (P)
The force per
unit area on a
surface

21. 21
Pressure is caused
by gas particles
slamming into the
container’s walls.

22. The common units of pressure are the
following:


Pascal (Pa) - standard unit of pressure
under Systemé International (SI) which is
equivalent to a force of one newton (1N = 1
kg m/s2) acting on an area of one square
meter.


Atmosphere (atm)


Torr


Millimeter mercury (mm Hg)

23. STP - Standard Temperature and
Pressure
Standard Temperature is 0°C
All temperature calculations in a gas must be in
Kelvin (K).
Reminder: K = C° + 273

24. Standard Pressure is 1 atmosphere
(atm) at sea-level
Helpful Hint: There is more than one type of
pressure unit. Here is the conversion factor.
1 atm = 760 mmHg = 101. 3 kPa

25. Pressure can be converted from
unit to another using the
following conversion:
•1 atm = 760 torr = 760 mm
Hg
•1 torr = 1 mm Hg
•1 atm = 101. 325 Pa

26. Converting between Units of Pressure:
atm., mmHg and kPa

27. One atm. equals 760.0 mm Hg, so there will be a multiplication or division based on the
direction of the change.
Example #1: Convert 0.875 atm to mmHg.
Solution: multiply the atm value by 760.0 mmHg / atm.
760.0 mmHg
0.875 atm x ––––––––––
1 atm

28. Example #2: Convert 745.0 mmHg to atm.
Solution: divide the mmHg value by 760.0 mmHg / atm
745.0 mmHg
––––––––––––––– = 0.980 atm
760.0 mmHg / atm

30. Solve (a) To convert atmospheres to torr, we use the
relationship 760 torr = 1 atm:

31. GAS
LAWS

32. A way to describe the characteristics of a gas as
conditions change.
For each gas law certain variables (amount,
temp., pressure, volume) change while others
are assumed to remain constant.

33. GAS LAWS
•Boyle’s Law
•Charles’ Law
•Gay-Lussac’s Law
•Combined Gas Law
•Ideal Gas Law
•Dalton’s Law of Partial Pressure
•Graham’s Law

34. Robert Boyle investigated the
relationship between the volume
of a gas and its pressure.
The other two variables, amount
and temperature, were assumed to
be constant (unchanged).

35. 35
Pressure and Volume: Boyle’s Law
How is the pressure applied to a gas related to its volume?
Piston
Gas molecules
Let’s apply pressure

36. 36
Pressure and Volume: Boyle’s Law
How is the pressure applied to a gas related to its volume?
Piston
Gas molecules
Piston
Gas molecules
Boyle’s Law: P
1V
1 = P
2V
2
Volume is inversely proportional to applied pressure.

37. 37
The Harder we Push
the smaller the gas
volume gets!
Boyle’s Law: P
1
V
1
= P
2
V
2

38. Boyle’s Results:
1. As pressure increases,
volume decreases.
2. As pressure decreases,
volume increases.
3. The volume of a fixed
amount of gas varies
inversely with the
pressure of the gas.

39. Boyles Law Equation:
P
1V
1 = P
2V
2

40. SAMPLE BOYLE’S LAW PROBLEM:
A sample of gas has a volume of 2.5 liters at a
pressure of 800 mmHg. What is the volume when
the pressure drops to 500 mmHg?
A sample of gas has a volume of 2.5 liters (V
1) at a
pressure of 800 mmHg (P
1
). What is the volume (V
2
)
when the pressure drops to 500 mmHg (P
2
)?

41. P
1V
1 = P
2V
2
IDENTIFY THE EQUATION YOU WILL
USE:
PLUG IN YOUR NUMBERS FROM THE
QUESTION:
(800 mmHg)(2.5L) = (500 mmHg)(V
2)
SOLVE: V
2
= 4L

42. 1. Boyle’s Law
•At a constant temperature, gas
pressure and volume are inversely
related.
•As one goes up the other goes
down
•Formula to use: P
1 x V
1= P
2 x V
2

43. 43
Boyle’s LawBoyle’s Law
A bicycle pump is a A bicycle pump is a
good example of good example of
Boyle’s law. Boyle’s law.
As the volume of the air As the volume of the air
trapped in the pump trapped in the pump
is reduced, its is reduced, its
pressure goes up, pressure goes up,
and air is forced into and air is forced into
the tire.the tire.

44. 44
A gas occupies a volume of
0.458 L at a pressure of 1.01 kPa and
temperature of 295 Kelvin. Although
the temperature stays the same, the
volume is increased to 0.477 L.
What is the new pressure?
0.970 kPa

45. •A balloon is filled with 25 L of air at 1.0 atm
pressure. If the pressure is changed to 1.5
atm what is the new volume?
Examples
P
1V
1 = P
2V
2
1.0 atm x 25 L = 1.5 atm x V2
1 atm x 25 L = 16.67L
1.5 atm

46. •A balloon is filled with 73
L of air at 1.3 atm
pressure. What pressure
is needed to change the
volume to 43 L?

47. 47
A balloon is filled with 73 L of air at 1.3
atm pressure. What pressure is needed to
change the volume to 43 L?
P
1V
1 = P
2V
2
1.3 atm x 73 L = P
2
x 43 L
1.3 atm x 73 L = 2.21 atm
43 L

48. Practice with Boyle’s Law
•A balloon contains 30.0 L of helium gas at 103
kPa. What is the volume of the helium when the
balloon rises to an altitude where the pressure is
only 25.0 kPa? (Assume temperature is held
constant)
P
1
V
1
= P
2
V
2
P
1 =
V
1
=
P
2
=
V
2 =

49. Practice with Boyle’s Law
At room temperature, 10.01 L of a gas is
found to exert 97.0 kPa. What pressure (in
atm) would be required to change the
volume to 5.00 L?
P
1
V
1
= P
2
V
2
P
1 =
V
1
=
P
2
=
V
2
=

50. Practice with Boyle’s Law
•Nitrous oxide (N
2
O) is used as an anesthetic. The
pressure on 2.50 L of N
2O changes from 105 kPa
to 40.5 kPa. If the temperature does not change,
what will the new volume be?
P
1
V
1
= P
2
V
2
P
1 =
V
1
=
P
2
=
V
2 =

51. 1. The volume of the lungs is measured by
the volume of air inhaled or exhaled.  If
the volume of the lungs is 2.400 L during
exhalation and the pressure is 101.70 KPa,
and the pressure during inhalation is
101.01 KPa, what is the volume of the
lungs during inhalation? 

52. 2. The total volume of a soda can is 415
mL Of this 415 mL, there is 60.0 mL of
headspace for the CO
2
gas put in to
carbonate the beverage.  If a volume of
100.0 mL of gas at standard pressure is
added to the can, what is the pressure in
the can when it has been sealed?

53. 3. It is hard to begin inflating a balloon.  A
pressure of 800.0 KPa is required to initially
inflate the balloon 225.0 mL.  What is the final
pressure when the balloon has reached it's
capacity of 1.2 L?

54. 4. If a piston compresses the air in the
cylinder to 1/8 it's total volume and the
volume is 930 cm
3
 at STP, what is the
pressure after the gas is compressed? 

55. 5. If a scuba tank that has a
capacity of 10.0 dm
3
  is filled
with air to 500.0 KPa, what will
be the volume of the air at 702.6
KPa? 

56. 56
Temperature and Volume: Charles’s Law
How is the volume of a gas related to its temperature?
gas molecules
moveable mass
(constant pressure)
What happens if heat is applied to the gas?

57. 57
Temperature and Volume: Charles’s Law
How is the volume of a gas related to its temperature?
gas molecules
moveable mass
(constant pressure)
Why did the volume change?
What happens to the average speed
of the gas molecules?
.

58. 58
Temperature and Volume: Charles’s Law
How is the volume of a gas related to its temperature?
gas molecules
moveable mass
(constant pressure)
Why did the volume change?
What happens to the average speed
of the gas molecules?
.

59. If I have 45 liters of helium in a balloon at 25
0
C and
increase the temperature of the balloon to 55
0
C,
what will the new volume of the balloon be?

60. Calcium carbonate decomposes at 1200
0
C to form carbon
dioxide and calcium oxide. If 25 liters of carbon dioxide are
collected at 1200
0
C, what will the volume of this gas be after
it cools to 25
0
C?

61. I have 130 liters of gas in a piston at a temperature of 250
0
C. If I
cool the gas until the volume decreases to 85 liters, what will
temperature of the gas be?

62. 62
Combined Gas Law (Boyle and Charles):

T
VP
T
VP
2
22
1
11
 T must be in Kelvin
Can be rearranged to:
P
1
V
1
T
2
= P
2
V
2
T
1
A combined gas law problem can be recognized by
having two sets of conditions.
Note: if one set of parameters is unchanged that term
will cancel on each side.

63. 63
A balloon contains helium gas with a volume of 2.60 L
at 25
o
C and 768 mmHg. If the balloon ascends to an
altitude where the helium pressure is 590 mmHg and the
temperature is 15
o
C, what is the volume of the balloon?
What type of
problem
is this?
There are 2 sets of
conditions.

64. A balloon contains helium gas with a volume of 2.60 L at
25
o
C and 768 mmHg. If the balloon ascends to an
altitude where the helium pressure is 590 mmHg and the
temperature is 15
o
C, what is the volume of the balloon?