Editing First law of thermodynamics
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Where ''U'' is the [[internal energy]] of the system, i.e. | Where ''U'' is the [[internal energy]] of the system, i.e. | ||
ignoring the external energy of the system, for example | ignoring the external energy of the system, for example | ||
motion of the | motion of the center of mass of the system, or the presence | ||
of an external field. ''Q'' is the | of an external field. ''Q'' is the [[heat]] and ''W'' is the [[work]]. | ||
For reversible changes | For reversible changes | ||
:<math>\left.dW\right.=-p~dV </math> | :<math>\left.dW\right.=-p~dV </math> | ||
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where <math>p</math> is the [[pressure]] and <math>V</math> is the volume. | where <math>p</math> is the [[pressure]] and <math>V</math> is the volume. | ||
For an adiabatic system (i.e. a system in which no heat enters or leaves) | For an adiabatic system (i.e. a system in which no heat enters or leaves) | ||
then if two bodies of different [[temperature |temperatures]] are placed in contact | then if two bodies of different [[temperature |temperatures]] are placed in contact | ||
and then separated then the sum of the heat within the system is unchanged | and then separated then the sum of the heat within the system is unchanged. | ||
This is conservation of energy. The first law of thermodynamics does not | This is conservation of energy. The first law of thermodynamics does not | ||
provide information on the direction of the heat transfer (if any). | provide information on the direction of the heat transfer (if any). | ||
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==References== | ==References== | ||
#[http://dx.doi.org/10.1098/rstl.1850.0004 James Prescott Joule "On the Mechanical Equivalent of Heat", Philosophical Transactions of the Royal Society of London '''140''' pp. 61-82 (1850)] | #[http://dx.doi.org/10.1098/rstl.1850.0004 James Prescott Joule "On the Mechanical Equivalent of Heat", Philosophical Transactions of the Royal Society of London '''140''' pp. 61-82 (1850)] | ||
[[Category: Classical thermodynamics]] | [[Category: Classical thermodynamics]] |