1. The Kinetic Molecular Theory Of Gases
Properties of Gases
The Kinetic Molecular Theory
Of Gases

2. What do you already know?
Shape
Volume
Movement
Particles
Temperature
Pressure

3. Real gas vs Ideal gas
There are many assumptions we make about how gases behave in order to apply simple math to them
Throughout the lecture, try to form an answer to this question:
Why do gases act most like ideal gases at high temperatures and low pressures?

4. Ideal Gas
An ideal gas is a gas that follows all the assumptions of the Kinetic Molecular Theory

5. Kinetic Molecular Theory: Overview
Describes how gas molecules behave under different conditions
Explains the physical properties that gases exhibit
Consists of 5 specific assumptions

6. 1st Assumption:
“Gases consist of large numbers of tiny particles that are far apart relative to their size”
What this means:
Molecules in gases are about 1000 times further apart from each other than liquid or solid molecules
Gases have extremely low densities

7. 2nd Assumption:
“Collisions between gas particles and between particles and container walls are elastic collisions.”
What this means:
Elastic collision - a collision in which there is no net loss of kinetic energy
Particles bounce apart
without loosing any of
their original energy or
momentum

8. 2nd Assumption: Elastic Collisions
The initial velocity of the gas
particles is the same velocity
they have after a collision
Because no energy is changed
when gas particles collide with
another object, they do not
interact permanently

9. 3rd Assumption: Particles continually move bounce and change direction
“Gas particles are in continuous rapid, random motion. They therefore posses kinetic energy, which is the energy of motion.”
What this means:
Gas particles are always moving
described as constant random motion
Gas particles move in all directions within their container
Particles continually move
bounce and change direction
within their container because
they posses kinetic energy

10. 4th Assumption: Particles continually move bounce and change direction
“There are no forces of attraction or repulsions between gas particles.”
What this means:
Gas particles are always moving
described as constant random motion
Gas particles move in all directions within their container
Particles continually move
bounce and change direction
within their container because
they posses kinetic energy

11. 5th Assumption:
“The average kinetic energy of gas particles depends on the temperature of the gas.”
What this means:
Temperature causes gas molecules to move more quickly
KE = 1/2 mv2
Higher velocity produces a higher kinetic energy
At the same temperature, lighter molecules move more quickly than heavier gas molecules

12. Properties that result from the KMT
Expansion
Diffusion
Effusion
Fluidity
Compressibility

13. Fluidity
Fluidity- molecules of gases flow across each other and throughout their container
Which assumption leads to this theory?
2nd assumption – elastic collisions between particles ensure they do not stick together
3rd assumption - gas particles are always moving

14. Compressibility
Compressibility – gas particles can be forced into a smaller space
Which assumption leads to this property?
1st assumption – particles are far apart so there is room to for them to fill

15. Expansion Gas will expand to fill their container
Which assumption leads to this property?
3rd assumption – gases are in constant random motion
The particles do not settle in any one space to create a definite volume
The particles in the solid and liquid settle at the bottom of the container, but the particles in the gas never stop moving and thus never settle

16. Diffusion
Diffusion – spontaneous mixing of the particles of two substances caused by their random motion
Gas particles will mix to fill their container
Which assumption leads to this principle?
3rd assumption – same as expansion

17. Effusion
Effusion – a process by which gas particles pass through a tiny opening
Which assumption leads to this property?
3rd assumption – because the gas particles are always moving they will eventually move to the location of the opening and go through it
We will go through effusion in much greater detail later