- #1
modulus
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- 3
This is more of a recurring conceptual doubt that I keep on running into when solving thermodynamics problems. We are taught that variations between extensive state variables in equilibrium are given by the following 'fundamental formula':
[tex]dE = TdS + \mathbf{J}\cdot{d}\mathbf{x} + \mathbf{\mu}\cdot{d}\mathbf{N}[/tex]
Now, in equilibrium, we also know that the internal energy [itex]E[/itex] is minimized; thus, first order variations in [itex]E[/itex] with respect to any variable will have to be equal to zero. But then I get weird results like this:
[tex]\frac{{\partial}E}{{\partial}S} = T = 0[/tex]
In fact, if I proceed like this I can show that all of the intensive variables will be zero in equilibrium, which clearly makes no sense.Where have I gone wrong?
[tex]dE = TdS + \mathbf{J}\cdot{d}\mathbf{x} + \mathbf{\mu}\cdot{d}\mathbf{N}[/tex]
Now, in equilibrium, we also know that the internal energy [itex]E[/itex] is minimized; thus, first order variations in [itex]E[/itex] with respect to any variable will have to be equal to zero. But then I get weird results like this:
[tex]\frac{{\partial}E}{{\partial}S} = T = 0[/tex]
In fact, if I proceed like this I can show that all of the intensive variables will be zero in equilibrium, which clearly makes no sense.Where have I gone wrong?