About Ensemble average

I need to calculate ensemble average of property enthalpy and internal energy. How is this possible?
Fix ave/time is not the ensemble average. right?

The answer to this question should be found in a statistical mechanics textbook.

It depends.

At any rate, this is not really a question about LAMMPS but about understanding statistical mechanics. After you have managed that, the answer to your second question should be obvious to you.

Thank you so much