Section 11­4.notebook
February 28, 2012
Entropy ­ a measure of the disorder of a system
Imagine 4 marbles 2 purple and 2 blue marbles. What are all the possible arrangements for the marbles?
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Section 11­4.notebook
February 28, 2012
Maximum entropy ­ when a system has reached a state of greatest disorder.
Imagine the marbles are put into a box purple on one side and blue on the other and shaken. The marbles are more likely to be mixed than unmixed.
The greater the probability the greater the entropy. Nature is lazy. Nature will always go to the state of the greatest possibility. Increasing disorder reduces the energy available for work.
­ Imagine the gas particles in an internal­combustion engine they do not all move in one direction when ignited. They will move all different directions rather than pushing all against the piston to produce more work.
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Section 11­4.notebook
February 28, 2012
Second Law of Thermodynamics can be expressed in terms of entropy. Take ice and melt it. In the phase of ice there is order with the arrangement of the molecules. When ice changes phase to a liquid the molecules can change order and location; increasing the amount of disorder. Entropy increases with heat added to a system. Thus heat and entropy are related. More heat there will be more entropy and vice versa.
The second law can be stated as follows: The entropy of the universe increases in all natural processes.
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Section 11­4.notebook
February 28, 2012
Entropy can increase or decrease within a system.
Take water in a freezer as work is done on the system to remove entropy from the water. However the environment will increase to offset the decrease in the water. The entropy is added to the air in the freezer. As the system's entropy decreases by some amount the entropy of the system's environment increases by a greater amount. This concept leads to the idea of the universe will eventually reach maximum entropy. At that time the universe will be in thermal equilibrium and the temperature will be uniform. Thus no transfer of energy as heat occurs and thus no work. This is referred to as ultimate "heat death" (estimate it will occur in 100 trillion years)
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Section 11­4.notebook
February 28, 2012
Section Review ­ #2­4
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