Observations and Second Law of Thermodynamics
| Thermodynamics | |
|---|---|
| Introduction | What is this thing called Thermodynamics??? | Definitions | Thermal Equilibrium and Zeroth Law | Limitations |
| First Law | Work, Heat, Energy, and the First Law | Work, Heat, Energy, and the First Law (simplied) | Derivatives | Derivatives Exercise | Reversibility, Enthalpy, and Heat Capacity |
| Second Law | Things to Think About | Observations and Second Law of Thermodynamics | Alternative Approach - the Clausis Inequality | Consequences of the Second Law | Consequences of the Second Law (simplified) | Carnot Principle - motivation and examples | Equivalence of Second Law Statements* |
| Third Law | Third Law of Thermodynamics | Consequences of Third Law* |
| Development of Thermodynamics | The Thermodynamic Network | Network Exercise | Equations of State (EOS) | EOS Example, Reading Tables, and Numerical Analysis | EOS Exercises | Thermochemistry |
* Optional Section | |
The second law of thermodynamics is based on observations of natural systems done back in the nineteenth century. This section will:
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Observation #1
Let us have a box with two sections separated by a removable partition. One side is filled with gas while the other is empty:
If we remove the partition, the gas disperses throughout the container:
However, we would have to wait a very, very, very long time for the gas to return all to one side so we can put the partition back in and get the original condition.[1] (We are assuming here a completely natural system with no external forces applied.)
We say a system like this tends toward disorder.
The measure of this disorder is called ENTROPY and given the symbol S.
Observation #2
Many processes have been developed which can convert work completely to heat. A simple example is by simply rubbing your hands the friction creates heat. However, no process has ever been developed which convert heat completely to work.
The first law says only that heat and work are both forms of energy. But it cannot explain the difference between them.
Second Law of Thermodynamics
We can combine these two observations into the The Second Law of Thermodynamics
- With no external input, a system will tend toward disorder
- No system can be developed which completely converts heat to work
We can prove that the two statements given here are equivalent. See here.
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Notes
- ↑ This is a classic problem in thermodynamics called Maxwell's Demon
