State function and Path function

• In thermodynamics, a state function, state quantity, or a function of the state, is a property of a system that depends only on the initial and final state the system, not on the way in which the system acquired that state.
• A state function describes the equilibrium state of a system and thus also describes the types of system.
• The cyclic integral involving a state function is always zero.
• All the thermodynamics property satisfy the requirements of state function.
• ∆U = q + w         change in thermodynamic energy
  S = q_rev/T            entropy
  H = U = PV         enthalpy
  G = H – TS          Gibb’s free energy
  A = U – TS          Helmholtz free energy
• Internal energy, enthalpy, entropy are the example of state functions.

Path Function:

• Path function depends on the path taken to reach that specific value, not on the initial and final state of that value.
• Path function needs multiple integral and limits of the integration in order to integrate.
• It is based on how the state of a system was established.
• Work, heat, arc length are the example of path function.