State Function and Path Function
The function which depends upon initial and final states of the system and not on how the change is carried out is called state function or point function. For example- the height from ground floor to fifth floor is a state function but the time taken to reach the fifth floor is a path function as time depends upon the means(i.e. stairs or lift) by which reach the fifth floor.
In terms of thermodynamics, if a system undergoes a series of processes and returns to its initial state, the change in the state function will be zero. State functions are additive, that means the total value of a state function for a composite system is the sum of the values of the state function for its individual components. State functions are differentiable because, their derivatives with respect to other state functions can be calculated.
Examples of State functions are- temperature, pressure, volume, Chemical composition, Mass, internal energy, enthalpy and entropy etc.
State function gives exact differentials. Such differentials can be integrated between limits without regards for the actual change that occurs as the system moves from one limiting condition to the other.
If a system undergoes a series of processes and returns to its initial state, the change in the path function will not necessarily be zero. Path functions are not additive, that means the total value of a path function for a composite system cannot be determined by simply sum up the values of the path function for its individual components. Path functions are not differentiable because, their derivatives with respect to other state functions cannot be calculated.
REMEMBER: State functions are path-independent properties of a system, while path functions are path-dependent properties of a system.
