1. Ideal Gases Kinetic Theory of Gases
Thermal Physics
Ideal Gases
Kinetic Theory of Gases

2. Ideal Gases – Variables
P is the ________
V is the ________
T is the ___________ (K)
n is the ________ of gas (moles)
For low P (low densities) the gas is called _____
Avogadro’s Number, NA, is the number of _________ per mole
Chosen so that the mass of NA particles is equal to _______ mass

3. n and Equation of State
Molar mass is the mass of ______ _______ of substance (use periodic table, e.g. SiO2→60 g/mol)
N is the number of molecules
Equation of State
Universal Gas Constant
Boltzmann’s Constant

4. Kinetic Theory – Assumptions
Large number of molecules – average separation _____ compared to their size.
Molecules obey Newton’s Laws , but motion is ______.
Molecules interact ___________ via short-range forces.
Molecules make _______ collisions with the walls of the container.
All molecules in a gas are _________.

5. Quantities Describing Gases
_____ Variables describe the macroscopic state of the gas:
Pressure P
Volume V
Temperature T
___________ Variables describe the individual molecules or atoms:
Mass m
Velocity v

6. Connecting Macroscopic to Microscopic – Pressured
Use ______-Momentum
Let Δt to be time for a round trip (1 collision with left wall for each round trip)
Fig , p. 341

7. Connecting Macroscopic to Microscopic – Pressure (cont’d)
Add contributions from all N molecules
Average value of squared velocity is
Total force is

8. Connecting Macroscopic to Microscopic – Pressure (cont’d)
Speed and the Pythagorean Theorem
Since motion in each direction is completely ______
Giving

9. Connecting Macroscopic to Microscopic – Pressure (cont’d)
Total force is
Divide by area A = d 2 to find the pressure

10. Ideal Gas Law – Revisited
Average translational kinetic energy per molecule
For monatomic gas

11. Root-Mean-Square Velocity
Connects macroscopic to microscopic
M is _____ mass in kg/mol