Zeroth Law of Thermodynamics

1. Zeroth Law of Thermodynamics P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Textbook of Materials & Metallurgical Thermodynamics by AhindraGhos An Universal Law for Measurement …

2. Scottish physicist Joseph Black • On returning to Glasgow as professor in 1756, Black met up with James Watt ("mathematical instrument maker to the University"). • This meeting stimulated the next phase of his work involving the concept of latent heat, and the first steps in calorimetry. • Here again, it was the quantitative aspects of his work which led to his discoveries, particularly in the careful measurement of heat. • "He waited with impatience for the winter" in Glasgow so that he could do experiments on the freezing and melting of water and water/alcohol mixtures that led to the concept of latent heat of fusion.

3. Scottish physicist Joseph Black in his (1786) Lectures on Chemistry, as such: • “[There exists] a tendency of heat to diffuse itself from any hotter body to the cooler around, • until it be distributed among them, in such a manner that none of them are disposed to take any more heat from the rest. • The heat is thus brought into a state of equilibrium. • This equilibrium is somewhat curious. • We find that when all mutual action is ended, a thermometer, applied to any one of the bodies, acquires the same degree of expansion: • therefore the temperature of them all is the same, and the equilibrium is universal.”

4. Equilibrium • Every system in this universe spontaneously move towards equilibrium. • Thermal equilibrium refers to equality of temperatures. • Thermal equilibrium is the subject of the Temperature measurement.

5. Zeroth Law of Thermodynamics • The "zeroth law" states that two thermodynamic systems in thermal equilibrium with the same environment are in thermal equilibrium with each other. • If A and C are in thermal equilibrium with B, then A is in thermal equilibrium with C. Maxwell [1872] • Practically this means that all three are at the same temperature. • A basis for comparison of effect of temperatures.

6. Demonstration of Zeroth Law When Two bodies have equality of temperature with a third body, they in turn have equality of temperature with each other. If the substance that composes the system is in thermal equilibrium, the temperature will be the same throughout the entire system, and we may speak of the temperature as a property of the system BRASS Copper

7. How Long it takes to achive Zeroth Law? Conservation of Energy during a time dt Heat in = Change in energy of thermocouple

8. Sudden Immersion of Thermometer in a Known Constant Temperature System Define Time constant

11. Response of A Thermo-couple in A Constant Temperature System

12. Response of A Thermo-couple in A Ramp Temperature System Ts(t)=Ct

13. Imapact of Zeroth Law: Creation of Temperatures

14. Outcome of Zeroth Law : Gas Thermometers

15. Further Experiments on Gas Thermometers p, kPa T (0C)

16. Further Experiments on Gas Thermometers Gas B Gas A p, kPa Gas C T (0C) Absolute Zero!

17. Further Experiments on Gas Thermometers : Unit mole of gas Gas A Gas C Gas B p, kPa T (0C) Absolute Zero!

18. Further Experiments on Gas Thermometers : Unit mole of gas p, kPa T (0C) Absolute Zero!

19. Saturated Liquid Nitrogen at 1 atm Saturated Liquid Nitrogen

21. A Journey tow Zeroards Absolute