Introductory Comments for Chapter 15
Thermodynamics
n Thermodynamics deals with the relationship between heat and mechanical energy.
n In thermodynamics we consider
Ø a system: the objects of interest.
Ø the environment: everything else
First Law of Thermodynamics
n It is a conservation of energy law that includes heat.
n The equation: DU = Q - W
n In words: The change in internal energy of a system (U) is equal to the heat added (Q) - the work done by the system (W)
Second Law of Thermodynamics
n It is a statement about which processes can occur in nature and which cannot.
n The second law goes beyond the limitations imposed by the first law and places constraints
Ø upon the direction of heat transfer
Ø the attainable efficiencies of heat engines.
n There are a number of equivalent ways of stating the second law
Ø Clausius's statement
Heat flows from a hot object to a cold object and never spontaneously from a cold object to a hot object.
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n Other statements of the second law
Ø Kelvin-Planck Statement
No process is possible whose sole result is the absorption of heat from a reservoir and the conversion of all of this heat into work.
Ø Carnot's Theorems
No engine can be more efficient that a reversible engine working between the same limits of temperature
All reversible engines working between the same two limits of temperature have the same efficiency
Ø In terms of entropy, which is a measure of disorder. The higher the entropy, the higher the disorder. For an isolated system, the entropy never decreases