Thermodynamics: Heat, Work, Thermodynamic definition of work, Types of work interaction, Point and Path functions, Examples for path functions are work and heat

Thermodynamics

Heat

It is the energy in transition between the system and the surroundings by virtue of the difference in temperature Heat is energy transferred from one system to another solely by reason of a temperature difference between the systems. Heat exists only as it crosses the boundary of a system and the direction of heat transfer is from higher temperature to lower temperature. For thermodynamics sign convention, heat transferred to a system is positive; Heat transferred from a system is negative.

Work

Thermodynamic definition of work

Positive work is done by a system when the sole effect external to the system could be reduced to the rise of a weight.

Work done by the system is positive and work done on the system is negative.

Types of work interaction

Expansion and compression work (displacement work)

Work of a reversible chemical cell

Work in stretching of a liquid surface

Work done on elastic solids

Work of polarization and magnetization

Point and Path functions

Point function

Point function does not depend on the history (or path) of the system. It only depends on the state of the system.

Examples of point functions are

temperature, pressure, density, mass, volume, enthalpy, entropy, internal energy etc.

Path function

Path function depends on history of the system (or path by which system arrived at a given state).

Examples for path functions are work and heat

Path functions are not properties of the system, while point functions are properties of the system.

Change in point function can be obtained by from the initial and final values of the function, whereas path has to defined in order to evaluate path functions.

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