Saturday, October 11, 2014

thermodynamics - Microscopic Definition of Heat and Work


If I am given a statistical system, then I can define state-variables like Energy, Entropy or other observables, and then I can (at least for equilibrium states) give the infinitesimal change of energy as:


$$ d E = T dS + K dx $$


Here x means any observable and K means the depending force, for example if x is the volume $V$, then K is minus the pressure $-p$. What I read all the time is


$$ d E = \delta Q + \delta W $$


Is there a general microscopic way to define what part of the above formula is $\delta W$ and what part is $\delta Q$ ?


For example, for reversible processes, $\delta Q = T dS$ and $\delta W = Kdx$. But what if I'm looking at an arbitrary process?




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