Aim:%20Students%20will%20be%20able%20to%20understand%20why%20gases%20behave%20the%20way%20they%20do%20by%20examining%20the%20Kinetic%20Molecular%20Theory - PowerPoint PPT Presentation

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Aim:%20Students%20will%20be%20able%20to%20understand%20why%20gases%20behave%20the%20way%20they%20do%20by%20examining%20the%20Kinetic%20Molecular%20Theory

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Aim: Students will be able to understand why gases behave the way they do by examining the Kinetic Molecular Theory Do Now: What is the total number of joules ... – PowerPoint PPT presentation

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Title: Aim:%20Students%20will%20be%20able%20to%20understand%20why%20gases%20behave%20the%20way%20they%20do%20by%20examining%20the%20Kinetic%20Molecular%20Theory


1
Aim Students will be able to understand why
gases behave the way they do by examining the
Kinetic Molecular Theory
  • Do Now What is the total number of joules
    absorbed by 65.0 g of water when the temperature
    of the water is raised from 25.0C to 40.0C?

2
Do Now
  • q mC?T
  • q (65.0g)(4.18 J/gC)(15.0C)
  • q 4076 J

3
Gases
  • Have you ever seen
  • a hot air balloon?
  • Have you ever opened a
  • shaken bottle of soda?
  • Why do they work the way they do?

4
In order to explain WHY gases work the way they
do
  • Scientists have come up with the.

5
KINETIC MOLECULAR THEORY
6
The Kinetic Molecular Theory describes the
behavior of gases
  • The KMT (kinetic molecular theory) describes the
    relationships among pressure, volume,
    temperature, velocity, frequency, and force of
    collisions.

7
Kinetic Molecular Theory
  • Particles in an ideal gas
  • have no volume.
  • have elastic collisions (there is no loss of KE)
  • are in constant, random, straight-line motion.
  • dont attract or repel each other.
  • have an avg. KE directly related to Kelvin
    temperature

8
Now that you know the laws that make up the
Kinetic Molecular Theory
  • You are ready to understand the relationships
    that make up the KMT.
  • Relationship between pressure and of particles
  • Relationship of pressure and volume of gas
  • Relationship of temperature and pressure of gas
  • Relationship of temperature and volume of gas
  • Relationship of temperature and velocity

9
Pressure
  • What is it?!

10
Pressure
  • Pressure is defined as the force the gas exerts
    on a given area of the container in which it is
    contained. The SI unit for pressure is the
    Pascal, Pa.
  • Pressure Force
  • Area
  • Units of pressure atmospheres (atm), torr,
    millimeters of Mercury (mmHg), and kilopascals
    (kPa)
  • Normal atmospheric pressure is 760 torr, 760
    mmHg, 1 atm, and 101.3 kPa

11
Pressure vs. Number of gas particles
  • What happens when you shake a full bottle of
    soda? What happens when you open it after shaking
    it?

12
Pressure vs. of gas particles
  • The pressure in the soda bottle builds up and if
    opened, the contents in the bottle rush out.

13
Pressure vs. of gas particles
  • Think about it!
  • Would a partially filled bottle of soda create a
    greater amount of pressure when shaken compared
    to a full bottle of soda?

14
Pressure vs. of gas particles
  • A filled bottle of soda would create more
    pressure when shaken due to the number of gas
    particles present inside and the increased number
    of collisions between those particles.
  • Gas particles not only collide with each other,
    but also with the walls of their container.
  • As the number of gas particles increases, the
    pressure increases.

15
Pressure vs. of gas particles
  • Basically, a container with more gas particles
    would have a greater pressure than a container
    with very few gas particles.
  • LESS Particles MORE Particles
  • LESS PRESSURE MORE PRESSURE

16
Boyles Law
  • States that there is an inverse relationship
    between the volume and pressure of a gas.

17
Relationship of pressure and volume of a gas
Boyles Law
  • Volume refers to the amount of space an object
    takes up.
  • For example, think about this classroom. Its
    volume is comfortable for us. Now, what would
    happen to us (the particles) if the walls began
    to close in?
  • Answer this question in terms of pressure!

18
Pressure vs. Volume Boyles Law
  • If the walls began to close in, particles would
    collide more with each other, causing pressure to
    increase.
  • So, as volume decreases, pressure increases.
  • PV k (a constant) P1V1 P2V2

19
Example of Boyles Law
  • Suppose that you have 5.00 liters of a gas at
    1.00 atm pressure, and then you decrease the
    volume to 2.00 liters. What is the new pressure?

20
  • Suppose that you have 5.00 liters of a gas at
    1.00 atm pressure, and then you decrease the
    volume to 2.00 liters. What is the new pressure?
  • P1V1 P2V2
  • (1.00 atm)(5.00 liters) P2 (2.00 liters)
  • Divide both sides by 2.00 liters to find P2
  • 5.00 atmliters P2 (2.00 liters)
  • 2.00 liters 2.00 liters

21
  • Suppose that you have 5.00 liters of a gas at
    1.00 atm pressure, and then you decrease the
    volume to 2.00 liters. What is the new pressure?
  • 5.00 atmliters P2 (2.00 liters)
  • 2.00 liters 2.00 liters
  • 2.50 atm P2

22
Relationship of Temperature and Pressure of a
Gas Gay-Lussacs Law
  • Recall the temperature of a substance is the
    measure of the average kinetic energy of its
    particles.
  • As temperature rises, what happens to the kinetic
    energy??

23
Relationship of Temperature and Pressure of a Gas
Gay-Lussacs Law
  • Yes, as temperature rises, the kinetic energy of
    particles increases.
  • As kinetic energy increases, the particles hit
    the walls of the container more frequently and
    with greater force.
  • So, as temperature increases, pressure increases.

24
Relationship of Temperature and Pressure of a
Gas Gay-Lussacs Law
  • Pressure is directly proportional to temperature.
  • P kT or P/T k
  • P1 P2
  • T1 T2

25
Example of Gay-Lussacs Law
  • As you have a tank of gas at 800 torr pressure
    and a temperature of 250 Kelvin, and its heated
    to 400 Kelvin, what is the new temperature?
  • P1 P2
  • T1 T2

26
  • As you have a tank of gas at 800 torr pressure
    and a temperature of 250 Kelvin, and its heated
    to 400 Kelvin, what is the new temperature?
  • P1 P2
  • T1 T2
  • (800 torr) P2
  • 250 K 400K
  • (800 torr)(400 K) P2 1280 torr
  • 250 K

27
Relationship between temperature and volume of a
gas Charless Law
  • At constant pressure (meaning, pressure does not
    change), as temperature increases, the molecules
    push harder against the walls of a container
    causing volume to increase.
  • As temperature increases, volume increases.
  • V/T b (where b is a constant)
  • V1/T1 b

28
Example of Charless Law
  • Suppose you live in Alaska and are outside in the
    middle of winter where the temperature is -23C.
    You blow up a balloon so that it has a volume of
    1.00 liter. You then take it inside your home
    where the temperature is a toasty 27C. What is
    the new volume of the balloon?
  • Charless Law V1/T1 V2/T2

29
  • Suppose you live in Alaska and are outside in the
    middle of winter where the temperature is -23C.
    You blow up a balloon so that it has a volume of
    1.00 liter. You then take it inside your home
    where the temperature is a toasty 27C. What is
    the new volume of the balloon?
  • V1/T1 V2/T2 (temp must be expressed in K)
  • -23C 273 250 K
  • (1.00 liter) V2 27C 273 300 K
  • (250 K) (300 K)

30
  • V1/T1 V2/T2
  • (1.00 liter) V2
  • (250 K) (300 K)
  • (1.00 liter)(300 K) V2 1.20 liters
  • 250 K

31
Relationship of Temperature and Velocity
  • As temperature increases, the kinetic energy
    increases.
  • Velocity refers to the speed of the particles
  • The higher the temperature, the greater the
    average velocity of the particles

32
Gas variables
  • VOLUME (V)
  • UNITS OF VOLUME (L)
  • AMOUNT (n)
  • UNITS OF AMOUNT (MOLES)
  • TEMPERATURE (T)
  • UNITS OF TEMPERATURE (K)
  • PRESSURE (P)
  • UNITS OF PRESSURE (mmHg)
  • UNITS OF PRESSURE (kPa)
  • UNITS OF PRESSURE (atm)
  • UNITS OF PRESSURE (torr)

33
A little review
  • BOYLES LAW
  • PRESSURE VOLUME
  • AS P? THEN V?
  • AT CONSTANT T, n

P1V1 P2V2
34
A Little review
  • GAY-LUSSACS LAW
  • TEMPERATURE PRESSURE
  • AS P? THEN T?
  • AT CONSTANT V, n

35
A Little review
  • CHARLES LAW
  • TEMPERATURE VOLUME
  • AS T? THEN V?
  • AT CONSTANT P, n

36
Another step up
  • If we combine all of the relationships from the 3
    laws covered thus far (Boyles, Charless, and
    Gay-Lussacs) we can develop a mathematical
    equation that can solve for a situation where 3
    variables change

PVk1
V/Tk2
P/Tk3
37
Combined gas law
  • AMOUNT IS HELD CONSTANT
  • IS USED WHEN YOU HAVE A CHANGE IN VOLUME,
    PRESSURE, OR TEMPERATURE

38
Combined gas law
  • AMOUNT IS HELD CONSTANT
  • IS USED WHEN YOU HAVE A CHANGE IN VOLUME,
    PRESSURE, OR TEMPERATURE

39
Example problem
A GAS WITH A VOLUME OF 4.0L AT STP. WHAT IS ITS
VOLUME AT 2.0ATM AND AT 30C?
1atm
2.0 atm
4.0 L
?
273K
30C 273
303K
40
PLUG CHUG
(1 atm)
(4.0L)
(2 atm)
( V )
2

(273K)
(303K)
2.22L V2
41
Gas laws deal with one other variable. We have
discussed Pressure Temperature Volume What
else do you think would effect HOW a gas behaves?
42
THE AMOUNT OF PARTICLES OF GAS This leads us to
AVOGADROS LAW (sounds kind of like avocado)
43
  • So far, weve compared all the variables except
    the amount of a gas (n).
  • There is a lesser known law called avogadros law
    which relates v n.
  • It turns out that they are directly related to
    each other.
  • As of moles increases then v increases.

V1 V2 n1 n2
V/n k
44
This leads us to the
45
The Ideal Gas Law
  • So far we have always held at least one of the
    variables constant.
  • Now, we can set up a much more powerful equation
    which can be derived by combining the proportions
    provided by the other laws weve studied
    recently.

46
The Ideal Gas Law Equation
  • PV nRT
  • where R is the universal gas constant.

47
The Ideal Gas Law
  • R is a constant that connects all four variables.
  • R is dependent on the UNITS of the variables for
    P, V, and T.
  • Temp is always in Kelvin
  • Volume is always in Liters
  • Pressure is either in atm, mmHg, kPa

48
  • BECAUSE OF THE DIFFERENT PRESSURE UNITS THERE ARE
    3 POSSIBILITIES FOR OUR R
  • IF PRESSURE IS GIVEN IN atm
  • IF PRESSURE IS GIVEN IN mmHg
  • IF PRESSURE IS GIVEN IN kPa

49
Using Ideal gas law
EG 1 WHAT VOL DOES 9.45g OF C2H2 OCCUPY AT
STP?
50
Using Ideal gas law
EG 1 WHAT VOL DOES 9.45g OF C2H2 OCCUPY AT
STP?
P ?
R ?
1atm
V ?
T ?
?
273K
n ?
.3635 mol
51
(1.0atm)
(V)

(.3635mol)
(273K)
V 8.15L
52
Using Ideal gas law
EG 2 A CAMPING STOVE PROPANE TANK HOLDS 3000g
OF C3H8. HOW LARGE A CONTAINER WOULD BE NEEDED
TO HOLD THE SAME AMOUNT OF PROPANE AS A GAS AT
25C AND A PRESSURE OF 303kPa?
53
Using Ideal gas law
P ?
R ?
303kPa
V ?
T ?
?
298K
n ?
68.2 mol
54
(303kPa)
(V)

(68.2mol)
(298K)
V 557.7L
55
Ideal versus Real Gases
  • Whats the difference?

56
What does the term ideal mean?
57
The ideal meal
58
The ideal weather
59
The ideal place to be instead of work/school
60
When something is ideal
  • It is the best, perfect option or idea for a
    particular situation.

61
Ideal versus Real Gases
  • The Kinetic Molecular Theory explains the
    behavior of gases using a model gas called an
    ideal gas.
  • When the gas laws are used to solve real problems
    using real gases, the results do not always
    match the results obtained in the lab.
  • This is because ideal gas model does not match
    the behavior of real gases.

62
Ideal vs. Real
63
When ideal gases do not match the behavior of
real gases
  • It is due to the fact that two of the assumptions
    made by the KMT are not exactly correct
  • - gas particles do not attract one another. (in
    extreme conditions, particles do attract each
    other)
  • - gas particles do not occupy volume. (while
    they typically occupy little to no volume, under
    high pressures, increased concentration of
    particles means far greater chances of combining)

64
What makes a gas truly ideal?
  • When it behaves exactly as predicted.
  • Gases vary from ideal behavior because of 2
    factors (increasing mass increasing polarity)
  • Gases are most ideal at low pressures and high
    temperatures.
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