Statistical mechanics

• What Is Chemical Potential in Thermodynamics?
  Chemical potential is the free-energy cost of adding matter. Learn its definitions, units, equilibrium role, and an ideal-gas example.
• How Is the Fermi–Dirac Distribution Derived?
  The Fermi–Dirac distribution follows by counting allowed fermion occupations and maximizing multiplicity: f(ε)=1/[exp((ε−μ)/kT)+1].
• Why Is Entropy an Extensive Quantity?
  Entropy is extensive because independent subsystems have multiplying numbers of microstates, and the logarithm turns that product into a sum.