Gitofa Shah PHYSICS   -   Statistical Mechanics

What is the name of the statistical mechanical potential that describes a system at constant temperature and pressure?

The Gibbs free energy is a statistical mechanical potential that describes a system at constant temperature and pressure, and is defined as G = H - TS, where H is the enthalpy and S is the entropy.
A system is in thermal equilibrium with a reservoir at temperature T. What is the probability of finding the system in a microstate with energy E? What is the name of the statistical ensemble that describes a system with a fixed number of particles, volume, and energy? What is the name of the theorem that relates the entropy of a system to the number of possible microstates? What is the name of the statistical mechanical potential that describes a system at constant temperature and pressure? A system undergoes a reversible adiabatic process. What is the change in entropy of the system?