Editing First law of thermodynamics
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Conservation of energy. | |||
:<math>\left.dU\right.= | :<math>\left.dU\right.=dQ+dW</math> | ||
Where | Where <math>U</math> 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. | of an external field. | ||
Reversible change | |||
:<math>\left.dW\right.=-PdV </math> | |||
irreversible change | |||
:<math>\left.dW\right. > -PdV </math> | |||
:<math>\left.dW\right. > - | |||
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 | then if two bodies of different 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). | ||
In other words, the common experience that the hotter object gives | In other words, the common experience that the hotter object gives | ||
heat to the colder object, the direction of heat flow from hot to cold, | heat to the colder object, the direction of heat flow from hot to cold, | ||
is left to the | is left to the second law of thermodynamics. | ||
== | |||
==Statistical mechanics== | |||
In [[statistical mechanics]] the internal energy is given by | |||
:<math>U=-T^2 \left. \frac{\partial (A/T)}{\partial T} \right\vert_{N,V} = k_B T^{2} \left. \frac{\partial \log Z(T)}{\partial T} \right\vert_{N,V}</math> | |||
[[Category: Classical thermodynamics]] | [[Category: Classical thermodynamics]] |