The First Law
The first law establishes that
Energy in a transformation is a “state function”, i.e., it only depends on the initial and final
state and not on the pathway used to reach the final state from the origin.
This is expressed by the equation:
DE ¼ DW þ DQ
where E is the internal energy, W is the work done, Q is the heat generated or
dissipated and the symbol D indicates the change of the property between the final
and the original state.
The Second Law
The second law is apparently more complex because it is less intuitive. It states that
the entropy of the Universe is a non-decreasing function of time,
DS Universe ! 0
The most prominent, and also the oldest expressions of the second law of
thermodynamics are formulated in terms of cyclic processes.
The Kelvin–Planck statement asserts that
no process is possible whose sole result is the extraction of energy from a heat bath, and the
conversion of all that energy into work.
The Clausius statement says
no process is possible whose sole result is the transfer of heat from a body of lower
temperature to a body of higher temperature.
Finally, the Carnot statement declares that
no engine operating between two heat reservoirs can be more efficient than a Carnot engine
operating between those same reservoirs.
The second law is expressed by the equation:
DS ¼ DQ=T
where S is the Entropy of the system, Q is the amount of Heat exchanged at the
temperature T.
234
Appendix B
The first law establishes that
Energy in a transformation is a “state function”, i.e., it only depends on the initial and final
state and not on the pathway used to reach the final state from the origin.
This is expressed by the equation:
DE ¼ DW þ DQ
where E is the internal energy, W is the work done, Q is the heat generated or
dissipated and the symbol D indicates the change of the property between the final
and the original state.
The Second Law
The second law is apparently more complex because it is less intuitive. It states that
the entropy of the Universe is a non-decreasing function of time,
DS Universe ! 0
The most prominent, and also the oldest expressions of the second law of
thermodynamics are formulated in terms of cyclic processes.
The Kelvin–Planck statement asserts that
no process is possible whose sole result is the extraction of energy from a heat bath, and the
conversion of all that energy into work.
The Clausius statement says
no process is possible whose sole result is the transfer of heat from a body of lower
temperature to a body of higher temperature.
Finally, the Carnot statement declares that
no engine operating between two heat reservoirs can be more efficient than a Carnot engine
operating between those same reservoirs.
The second law is expressed by the equation:
DS ¼ DQ=T
where S is the Entropy of the system, Q is the amount of Heat exchanged at the
temperature T.
234
Appendix B