1. Thermodynamic Processes
Chapter 10

2. Work at Constant Pressure
Constant Pressure Work
The definition of work becomes W=Fd for a constant force F along a distance d. Using the definition of pressure, can we deduce a formulae for the work done by the piston below?

4. The First law of Thermodynamics

6. In the data booklet as…

7. Why the changes in signs?!
It’s important to get the positive and negatives right here…
If Q is positive – HEAT ENERGY is being added TO the system
If Q is negative – HEAT ENERGY is being LOST by the system

8. If work is negative – WORK is being done ON the system (the gas is being compressed)
If work is positive – WORK is being done BY the system (the gas is expanding)
If U is positive – GAIN in internal energy of the gas
If U is negative – LOSS in internal energy of the gas

9. Definitions
Isochoric – (Isovolumetric) A change that takes place at constant volume
Isobaric – A change that takes place at constant pressure
Isothermal – A change that takes place at constant temperature

10. Which graph shows which change?!
In which process would the work done be zero?
How would you work out the work done during the process?

11. One more…
Adiabatic- A change in the gas where no energy enters or leaves the system
Q= 0

12. Adiabatic Process
Adiabatic process must take place rapidly and the system is not in thermal equilibrium with its surroundings
Any RAPID expansion or compression CAN be assumed to be ADIABATIC (Q=0)

13. First Law of Thermodynamics
Is just the Conservation of Energy law in a different format!

14. Heat engines!

15. Heat Engines
Usually depicted like the diagram below

16. Carnot Cycle- most efficient cycle (imaginary)

17. Otto Cycle

18. Heat Pump (Refrigerator)

19. Second Law of Thermodynamics
Many ways of saying this!!
Thermal energy may be completely converted to work in a single process, but that continuous conversion of this energy into work requires a cyclical process and the transfer of some energy from the system.
Thermal energy can not be spontaneous transferred from a region of cold temperature to a region of hot temperature

20. Entropy and the Second Law
The second law of thermodynamics states that the entropy of an isolated system never decreases, because isolated systems spontaneously evolve toward thermodynamic equilibrium—the state of maximum entropy.

21. Entropy Is a measure of the degree of disorder of a system.
Although local entropy may decrease (heat pumps), any process will increase the total entropy of the system and surroundings, that is, the universe.
The overall entropy of the universe is increasing.
All natural processes increase the entropy of the universe.

22. Entropy
The change in Entropy when a quantity of heat energy flows into a body is equal to…
ΔS = Q/T
Units?!

23. Entropy