1. 13 Temperature and Ideal Gases
Homework:
Problems: 1, 7, 41.
Thermal Equilibrium
Temperature Scales
Ideal Gases
Thermal Expansion

2. Temperature T ~ avg. KE/molecule Thermal Expansion Scales: Kelvin, K
C° = K – 273
F° = (9/5)C° + 32 2 2

3. Thermal Equilibrium Heat flows from hotter object to cooler object.
When the heat flow ceases the objects are in thermal equilibrium.
Objects in thermal equilibrium are at the same temperature. /

4. Ideal Gas

5. Gas Thermometer PV ~ NT P ~ T (V, N constant) Gas cools, avg. KE  0,
(absolute zero),
P  0,
≈ -273 °C

6. Constant Pressure
What % increase in V occurs for an ideal gas heated from 20C to 40C? (V ~ T)
(It does not double, b/c C is not a thermodynamic temperature scale)
V2/V1 = T2/T1 = (273+40)/(273+20) = 1.068
6.8% increase in volume.

7. Linear Thermal Expansion
DL = a Lo DT
Example: 100C increase in Aluminum causes a fractional increase in length of = 0.24% change.

8. Bi-Metallic Strips

9. Summary Thermal Equilibrium Temperature Scales Ideal Gases
Thermal Expansion

10. Water Expansion Expansion from 4°C to 100°C (normal)
Contraction from 0°C to 4°C. (anomalous, transient ice melting) 10 10 10 10

11. 11 11 11 11

12. Superheating
Mythbusters 12 12

13. Ideal Gases N molecules (few intermolecular collisions)
v = average speed
P due to wall-collisions (P ~ Nv/t)
t = time between same-wall collision

14. Ideal gas pressure

15. Ideal Gas Law