1. How do we use the Kinetic Molecular Theory to explain the
behavior of gases?
Introduction to Gases
https://www.sisd.net/cms/lib/TX01001452/Centricity/Domain/382/Intro%20to%20Gases%
20and%20Gas%20Laws.ppt
2. States of Matter
•There are two main factors determine the 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
Atkins, P.W.; Jones, Loretta Chemistry Molecules, Matter and Change 4th Ed. . July 2000
3. Kinetic Energy , States of Matter & Temperature
• Gases tend to have more higher kinetic energy in their molecules
due to weak bonding as compare to solid and liquid.
• On increase the temperature, the gas particles move faster, and
thus kinetic energy increases in the system.
4. Characteristics of Gases
• Gases can expand to fill any container to any
shape.
• They have random motion, no attraction in their
particles
• Gases are fluids (like liquids).
• There is no attraction in their molecules/atoms.
• 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,
• how air conditioner works?
Hint: Compressor role?
• Gases undergo diffusion & effusion (across a barrier with small
holes).
• random motion
• How perfume molecules spread, from high concentration to low
concentration.
6. Kinetic Molecular Theory of ‘Ideal’ Gases
• Particles in an ideal gas…
• They have no volume or no shape.
• They have elastic collisions (ie. billiard ball/snooker
particles exchange energy with each other, but total KE
is conserved in the system.
• They have constant, random, straight-line motion, no
circular motion.
• They don’t attract or repel each other, no attraction
between molecules.
• They have avg. KE directly related to temperature, it is
directly proportional, if one parameter increases then
other one will also increase.
Atkins, P.W.; Jones, Loretta Chemistry Molecules, Matter and Change 4th Ed. . July 2000
7. Real Gases
• The behavior of particles in a REAL gas condition
• They have their own volume
• They attract each other (intermolecular forces)
• Gas behavior is found most ideal…
• at low pressures
• at high temperatures (high KE)
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
10. Atmospheric Pressure
•The gas molecules in the atmosphere are pulled
toward Earth due to gravity, exerting pressure
•Ears ‘pop’ in an airplane or at high mountain or
high rise building/skycrappers?
12. Units of Pressure
•At Standard Atmospheric Pressure (SAP)
101.325 kPa (kilopascal)
1 atm (atmosphere)
760 mm Hg
(millimeter Hg)
760 torr
14.7 psi (pounds per square inch)
2
m
N
kPa
13. Temperature: The Kelvin Scale
• Always use absolute temperature (Kelvin) when working with gases.
ºC
K
-273 0 100
0 273 373
273
K
C K = ºC + 273
14. 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:
http://www.youtube.com/watch?v=JHXxPnmyDbk
• Comparing the Celsius and Kelvin Scale:
http://www.youtube.com/watch?v=-G9FdNqUVBQ
18. 1. Intro to Boyle’s Law
•Suppose that you hold the syringe by your hand and
there should be no leak from the cylinder or body of
syringe, no gas can release. Now push down on the
piston of the syringe in and out.
Is it any changes in the volume inside the syringe?
Do you feel pressure of the gas is exerting in the
syringe during the pressing of piston?
20. 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 temp
P
V
General chemistry- Principles, patterns and Applications. Bruce Averill, Strategic Energy
Security Solutions. Patricia Eldredge, R.H. Hand, LLC ISBN 13: 9781453322307. Saylor
Foundation. Pages: 186-222
21. 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
22. Example Problem:
A hot balloon having a vol of 4000 L at pressure of 100.0 kPa rises to an
altitude of 2000 m, where the atm pres is found to be 50.2 kPa. There is
no change in the temp and the amount of gas, find the balloon’s final vol.
23. V
T
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
https://www.sisd.net/cms/lib/TX01001452/Centricity/Domain/382/Intro%20to%20Gases%20
and%20Gas%20Laws.ppt
25. 2. Charles’ Law
• Charles’ Law leads to the mathematical
expression:
*Assuming pressure remains constant
26. 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?
27. Example Problem:
John filled the balloon with helium gas, having volume of 3.0 L in an air-
conditioned room at 300 K. Then, he took the balloon outdoors on a warm day
where the volume change or expands to 3.25 L. Suppose the pres and the vol of
gas is constant, find the air temperature?
A volley ball is inflated to a vol of 50 L of air at 30 oC. During the afternoon,
the volume increases by 2 L. Find the new temperature outside?
28. 3. Intro to Gay-Lussac’s Law
• Suppose you have a balloon that it has a fixed volume.
• You heat the balloon.
What is change in the temp of gas inside the balloon?
Any change will happen to the pressure, the gas is exerting on
the balloon?
29. P
T
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
30. 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:
http://www.youtube.com/watch?v=r_JnUBk1JPQ
31. 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.
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?
32. 4. Combined Gas Law
P1V1
T1
=
P2V2
T2
By combining Boyle’s, Charles’ and Gay
Lussac’s Laws, the following equation is
derived:
A gas occupies 7.84 cm3 at 71.8 kPa & 25°C. Find its
volume at STP.
33. References
1. General chemistry- Principles, patterns and Applications. Bruce
Averill, Strategic Energy Security Solutions. Patricia Eldredge, R.H.
Hand, LLC ISBN 13: 9781453322307. Saylor Foundation. Pages: 186-
222
2. East, T.D and McConkey, A (1996), Applied Thermodynamics for
Engineering Technologists.5thEd,Longman.
3. Atkins, P.W.; Jones, Loretta Chemistry Molecules, Matter and
Change 4th Ed. . July 2000
Useful link: http://readinglists.central-lancashire.ac.uk/index
