Q.What are State and Path Functions ? Give two examples.

A state function's value is fixed by the current state of the system alone; a path function's value depends on how the system got there -- internal energy/enthalpy are state functions, heat/work are path functions.

State functions:

A state function (or state variable) is a thermodynamic property whose value depends only on the current state of the system (e.g. its temperature, pressure, volume, composition), not on the path or process by which that state was reached. Consequently, the change in a state function between an initial and final state (Delta-X = X_final - X_initial) is always the same, no matter what path connects the two states.

Examples: Internal energy (U), Enthalpy (H), Entropy (S), Gibbs free energy (G), pressure (P), volume (V), temperature (T).

Path functions:

A path function is a quantity whose value depends on the specific path or process taken to go from the initial state to the final state -- it is not a property of the state itself, and it doesn't make sense to talk of a system "having" a certain amount of it at a given state (only an amount transferred during a process).

Examples: Heat (q), Work (w).

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