Wednesday, August 31, 2016

thermodynamics - Is delta Q – delta W a state function?


I know that internal energy, Q+W is a state function. But dU=\delta Q-\delta W,
is the change in internal energy, where dU is change in internal energy, \delta Q is the heat supplied to the system and \delta W is the work done by the system. Is this a state function too?




Answer



The quantity dU=\delta Q-\delta W is not a state function simply because it is not a function, it is a differential of a function. In that case a differential of the state function U.


The fact that there is a function U such that the differential \delta Q-\delta W is the differential of U means that the differential is exact or U is a state function, i.e., it has a definite value for every point in the space of configuration. In another words, the change in energy depends only on the initial and final states.


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