Today I've got rid of a lot of questions but one remains so far.
The definition of temperature I've seen in Callen's book is ##T=\left ( \frac{\partial U}{\partial S} \right ) _{V, \{ n_i \} }## (i=1, 2, etc.) where the entropy is defined only for equilibrium states.
Therefore if I understand well, T is also defined only for equilibrium states. However in the lab. or in everyday's life (meteorogolists), we all use temperature as if it was defined even for systems that are totally off from any thermodynamic equilibrium. How is that possible? Does it even make sense to talk about temperature for systems that aren't in thermodynamics equilibrium, i.e. systems that have not a well defined entropy?
The definition of temperature I've seen in Callen's book is ##T=\left ( \frac{\partial U}{\partial S} \right ) _{V, \{ n_i \} }## (i=1, 2, etc.) where the entropy is defined only for equilibrium states.
Therefore if I understand well, T is also defined only for equilibrium states. However in the lab. or in everyday's life (meteorogolists), we all use temperature as if it was defined even for systems that are totally off from any thermodynamic equilibrium. How is that possible? Does it even make sense to talk about temperature for systems that aren't in thermodynamics equilibrium, i.e. systems that have not a well defined entropy?