Zeroth Law of Thermodynamics

1. Zeroth Law of Thermodynamics

2. The Concept of Temperature • The concept of temperature is an afterthought in scientific history • By the time a truly usable standard unit for measuring temperature came along, the 1st and 2nd law of thermodynamics were quite well established

3. The Concept of Temperature • Imagine not knowing anything about temperature while conducting thermal experiments with heat and closed containers. • Mechanical equilibrium: balance achieved between two systems attempting to do work on one another • The most interesting thing to witness as a thermodynamisist is nothing!

4. The Concept of Temperature • Envision two pressurized chambers connected with a moveable piston between them held in place with a pin. • Three reactions are possible when pin is removed. • Piston moves toward chamber A • Piston moves toward chamber B • PISTON DOES NOT MOVE!

5. The Concept of Temperature • Assuming that chamber B is of known pressure, what can we say about the pressure of chamber A if the piston moves into chamber B? • what can we say about the pressure of chamber B and chamber A if the piston does not move when the pin is removed?

6. The Concept of Temperature • If we test another chamber C of unknown pressure against chamber B and find that the piston does not move, what can we say about the pressure of chamber C and chamber A? • Therefore, under these conditions, A = B = C. • If the piston moves, Pressure \ Volume Work has been done. • If the piston does not move, the systems are in mechanical equilibrium.

7. The Concept of Temperature • Thermal equilibrium is the balance achieved between two systems attempting to exchange heat with one another. • The same process observed with pressure \ volume experiments can be applied to the measurement of the internal energy in a system using the flow of heat.

8. The Concept of Temperature • Energy transfers were among the first physical properties to be qualified using primitive measuring techniques. • They were also among the first thermodynamic properties to be quantified using advancing measurement equipment.

9. The Concept of Temperature • Earliest thermal measuring devices were diathermic which means they conduct heat like a saucepan. • If a sealed diathermic system is placed against a material of unknown thermal content, the change in the diathermic system reveals a referenced thermal content.

10. Development of Temperature Scales • Celcius: scale set at 0 for water freezing and 100 for water boiling. • Fahrenheit: scale set at 0 for the coldest temperature attainable in a salt water mixture. Water freezes at 32 and boils at 212.

11. Jacques Charles (1746-1823) • Charles discovered the relationship between temperature and volume in 1787. • He found that all gases expand to the same extent when heated through the same temperature range. • A volume of a gas heated or cooled by one degree celcius changes by 1/273 of the original volume. • This property was used to create the Kelvin scale.

12. Boltzman (1844-1906) • He theorized that molecules in a system exist within specific energy levels. • In his model, an isolated group of molecules or atoms have a range of energies based on their transitional, rotational, and vibrational motions.

13. Boltzman • It would be too much work to calculate the energy of each particle separately • Therefore to simplify things, we can use the average energy of the collection in calculations • Boltzman describes the behavior of these particles with the Boltzman distribution (β)

14. Boltzman • β could have been used as our measure of temperature had Ludwig done his work before Celcius and Fahrenheit. • Instead, the Boltzman constant is used to convert β into units with Kelvin.

15. Boltzman • The Boltzman Distribution shows the average number of molecules at each energy level in a system at a given temperature • High β is low temperature • Low β is high temperature • Water freezes at β = 2.65 x 1020J-1 and boils at 1.94 x 1020J-1