Contributed by:
The highlights are:
1. States of matter
2. Characteristics of gases
3. Kinetic theory of gases
4. Real gases
5. Pressure
6. Boyle law
7. Charles law
8. Gay-Lussac's law
9. Combined gas law
1.
Introduction to
Gases
EQ:
How do we use the
Kinetic Molecular
Theory to explain the
behavior of gases?
2.
States of Matter
2 main factors determine state:
• The forces (inter/intramolecular) holding particles together
• The kinetic energy present (the energy an object possesses due to its motion of the particles)
• KE tends to ‘pull’ particles apart
3.
Kinetic Energy , States of Matter &
Temperature
Gases have a higher kinetic energy because their particles move a lot more than
in a solid or a liquid
As the temperature increases, there gas particles move faster, and thus kinetic
energy increases.
4.
Characteristics of Gases
Gases expand to fill any container.
• random motion, no attraction
Gases are fluids (like liquids).
• no attraction
Gases have very low densities.
• no volume = lots of empty space
5.
Characteristics of Gases
Gases can be compressed.
• no volume = lots of empty space
Gases undergo diffusion & effusion (across a barrier with small holes).
• random motion
6.
Kinetic Molecular Theory of
‘Ideal’ Gases
Particles in an ideal gas…
• have no volume.
• have elastic collisions (ie. billiard ball
particles exchange energy with eachother,
but total KE is conserved
• are in constant, random, straight-line motion.
• don’t attract or repel each other.
• have an avg. KE directly related to
temperature ( temp= motion= KE)
7.
Real Gases
Particles in a REAL gas…
• have their own volume
• attract each other (intermolecular forces)
Gas behavior is most ideal…
• at low pressures
• at high temperatures
Why???
8.
Real Gases
At STP, molecules of gas are moving fast and are
very far apart, making their intermolecular forces
and volumes insignificant, so assumptions of an
ideal gas are valid under normal temp/pressure
conditions. BUT…
• at high pressures: gas molecules are pushed
closer together, and their interactions with each
other become more significant due to volume
• at low temperatures: gas molecules move
slower due to KE and intermolecular forces
are no longer negligible
9.
Pressure
force
pressure
area
Which shoes create the most pressure?
10.
Atmospheric Pressure
The gas molecules in the atmosphere are pulled
toward Earth due to gravity, exerting pressure
Why do your ears ‘pop’ in an airplane?
11.
Pressure
Barometer
• measures atmospheric pressure
Mercury Barometer
12.
Units of Pressure
At Standard Atmospheric Pressure (SAP)
101.325 kPa (kilopascal)
1 atm (atmosphere)
760 mm Hg
(millimeter Hg) N
760 torr kPa 2
m
14.7 psi (pounds per square inch)
13.
Standard Temperature &
STP
Standard Temperature & Pressure
0°C 273 K
-OR-
1 atm 101.325 kPa
14.
Temperature: The Kelvin
Always use absolute temperature
(Kelvin) when working with gases.
-273 0 100
K
0 273 373
C K 273 K = ºC + 273
15.
Kelvin and Absolute Zero
Scottish physicist Lord Kelvin suggested that -273oC (0K) was the temperature at which the motion particles within a
gas approaches zero.. And thus, so does volume)
Absolute Zero:
Comparing the Celsius and Kelvin Scale:
16.
Why Use the Kelvin Scale?
Not everything freezes at 0oC, but for ALL substances, motion stops at 0K.
It eliminates the use of negative values for temperature! Makes mathematic
calculations possible (to calculate the temp. twice warmer than -5 oC we can’t use
2x(-5oC) because we would get -10oC!)
17.
Kelvin Scale vs Celsius Scale
18.
Converting between Kelvin and
Celsius
C K 273 K = ºC + 273
a) 0oC =_____K
b) 100oC= _____K
c) 25oC =______K
d) -12oC = ______K
e) -273K = ______oC
f) 23.5K = ______oC
g) 373.2K= ______oC
19.
How Did We Do So
Far?
Learning Goal:
I will be able to
understand what kinetic
energy is and how it
relates to gases and
temperature, describe
the properties of a real
and ideal gas and
understand what
Absolute Zero is and
how to convert between
the Kelvin and Celsius
20.
Part B: The Gas
Laws
Part B:
Learning Goals
I will be able to
describe Boyle’s,
Charles’ and Gay-
Lussac’s Laws
relating T, P and/or
V and be able to
calculate unknown
values using the
equations derived
from these laws, as
well as the
21.
1. Intro to Boyle’s Law
Imagine that you hold the tip of a syringe on the tip of your finger
so no gas can escape. Now push down on the plunger of the
syringe.
What happens to the volume in the syringe?
What happens to the pressure the gas is exerting in the syringe?
23.
1. Boyle’s Law
The pressure and volume of a gas are
inversely proportional (as one increases,
the other decreases, and vice versa
• at constant mass & temp
V
24.
1. Boyle’s Law
Boyle’s Law leads to the mathematical
expression: *Assuming temp is constant
P1V1=P2V2
Where P1 represents the initial pressure
V1 represents the initial volume,
And P2 represents the final pressure
V2 represents the final volume
25.
Example Problem:
A weather balloon with a volume of 2000L at a pressure of 96.3
kPa rises to an altitude of 1000m, where the atmospheric pressure
is measured to be 60.8kPa. Assuming there is no change in the
temperature or the amount of gas, calculate the weather balloon’s
final volume.
26.
You Try:
Atmospheric pressure on the peak of Kilimanjaro can be as low as
0.20 atm. If the volume of an oxygen tank is 10.0L, at what
pressure must the tank be filled so the gas inside would occupy a
volume of 1.2 x 103L at this pressure?
27.
2. Intro to Charles’ Law
Imagine that you put a balloon filled with gas in liquid nitrogen
What is happening to the temperature of the gas in the
balloon?
What will happen to the volume of the balloon?
29.
2. Charles’ Law
The volume and absolute temperature (K) of
a gas are directly proportional (an increase
in temp leads to an increase in volume)
• at constant mass & pressure
T
31.
2. Charles’ Law
Charles’ Law leads to the mathematical
expression:
*Assuming pressure remains constant
32.
Example Problem:
A birthday balloon is filled to a volume of 1.5L of helium gas in an
air-conditioned room at 293K. The balloon is taken outdoors on a
warm day where the volume expands to 1.55L. Assuming the
pressure and the amount of gas remain constant, what is the air
temperature outside in Celsius?
33.
You Try:
A beach ball is inflated to a volume of 25L of air at 15oC. During
the afternoon, the volume increases by 1L. What is the new
temperature outside?
34.
3. Intro to Gay-Lussac’s
Imagine you have a balloon inside a container that ensures it
has a fixed volume. You heat the balloon.
What is happening to the temp of the gas inside the balloon?
What will happen to the pressure the gas is exerting on the
balloon?
35.
3. Gay-Lussac’s Law
The pressure and absolute temperature
(K) of a gas are directly proportional (as
temperature rises, so does pressure)
• at constant mass & volume
T
36.
2. Gay-Lussac’s Law
Gay-Lussac’s Law leads to the mathematical
expression:
*Assuming volume remains constant
Egg in a bottle to show Gay-Lussac's Law:
T & P relationship:
37.
Example Problem:
The pressure of the oxygen gas inside a canister with a fixed
volume is 5.0atm at 15oC. What is the pressure of the oxygen gas
inside the canister if the temperature changes to 263K? Assume
the amount of gas remains constant.
38.
You Try:
The pressure of a gas in a sealed canister is 350.0kPa at a room
temperature of 15oC. The canister is placed in a refrigerator that
drops the temperature of the gas by 20K. What is the new
pressure in the canister?
39.
4. Combined Gas Law
By combining Boyle’s, Charles’ and Gay
Lussac’s Laws, the following equation is
P1V1 P2V2
=
T1 T2
40.
Example Problem:
A gas occupies 7.84 cm3 at 71.8 kPa & 25°C. Find
its volume at STP.
41.
Any Combination
Questions
a) A gas occupies 473 cm3 at 36°C. Find its volume at 94°C
b) A gas’ pressure is 765 torr at 23°C. At what temperature will the
pressure be 560. torr
42.
How Did You Do?
Part B:
Learning Goals
I will be able to
describe Boyle’s,
Charles’ and Gay-
Lussac’s Laws
relating T, P and/or
V and be able to
calculate unknown
values using the
equations derived
from these laws, as
well as the
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