Path and Point Functions in Thermodynamics

In thermodynamics, there are two types of functions that are used to describe the state of a system: path functions and point functions. Path functions depend on the path taken to reach a certain state, while point functions depend only on the state of the system and not on how it got there.

Path Functions:

Path functions are also known as process functions. They are properties that depend on the path taken to reach a certain state. Path functions describe the energy transfer that occurs during a process. Examples of path functions include work and heat.

Work: Work is the energy transfer that occurs during a mechanical process. It is defined as the force applied to an object multiplied by the distance the object moves in the direction of the force. Work is a path function because it depends on the path taken to reach a certain state.

Heat: Heat is the energy transfer that occurs between a system and its surroundings due to a temperature difference. Heat is also a path function because it depends on the path taken to reach a certain state.

Extensive Properties:

Extensive properties are properties that depend on the amount of material in a system. Examples of extensive properties include mass, volume, and energy. Extensive properties are additive, which means that the value of the property for the entire system is equal to the sum of the values of the property for each individual part of the system.

Intensive Properties:

Intensive properties are properties that do not depend on the amount of material in a system. Examples of intensive properties include temperature, pressure, and density. Intensive properties are not additive, which means that the value of the property for the entire system is not equal to the sum of the values of the property for each individual part of the system.

Point Functions:

Point functions are also known as state functions. They are properties that depend only on the state of the system and not on how it got there. Point functions describe the state of a system. Examples of point functions include internal energy, enthalpy, and entropy.

Internal Energy: Internal energy is the sum of the kinetic and potential energies of the particles in a system. Internal energy is a point function because it depends only on the state of the system and not on how it got there.

Enthalpy: Enthalpy is the sum of the internal energy of a system and the product of its pressure and volume. Enthalpy is also a point function because it depends only on the state of the system and not on how it got there.

Entropy: Entropy is a measure of the disorder or randomness of a system. Entropy is a point function because it depends only on the state of the system and not on how it got there.

See, the basic logic by which I remember this is that we have different formulas to calculate the amount of work in different processes between the same initial and final points. This means that work doesn't depend on the initial and final points but depends on the path followed, hence it is a path function and not a point function.