# Work (thermodynamics)

workthermodynamic workpressure-volume workuseful workheatPVthermodynamical
In thermodynamics, work performed by a system is energy transferred by the system to its surroundings, by a mechanism through which the system can spontaneously exert macroscopic forces on its surroundings, where those forces, and their external effects, can be measured.wikipedia
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### Thermodynamics

thermodynamicthermodynamicallyclassical thermodynamics
In thermodynamics, work performed by a system is energy transferred by the system to its surroundings, by a mechanism through which the system can spontaneously exert macroscopic forces on its surroundings, where those forces, and their external effects, can be measured.
Thermodynamics is the branch of physics that deals with heat and temperature, and their relation to energy, work, radiation, and properties of matter.

### Energy

energy transferenergiestotal energy
In thermodynamics, work performed by a system is energy transferred by the system to its surroundings, by a mechanism through which the system can spontaneously exert macroscopic forces on its surroundings, where those forces, and their external effects, can be measured.
In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object.

### Heat

heat energythermalhot
When it is done isochorically, and no matter is transferred, such an energy transfer is regarded as a heat transfer into the system of interest.
In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter.

### Isochoric process

isochoricconstant volumeisochoric flow
The paddle stirring experiments of Joule provide an example, illustrating the concept of isochoric (or constant volume) mechanical work, in this case sometimes called shaft work.
The process does no pressure-volume work, since such work is defined by

### Mechanical equivalent of heat

Circa 1797, Count Rumford (born Benjamin Thompson)heat generated by mechanical workmechanical equivalence of heat
Using these values, Joule was able to determine the mechanical equivalent of heat.
In the history of science, the mechanical equivalent of heat states that motion and heat are mutually interchangeable and that in every case, a given amount of work would generate the same amount of heat, provided the work done is totally converted to heat energy.

### First law of thermodynamics

firstenergy balancechange in temperature
For a process in a closed (no transfer of matter) thermodynamic system, the first law of thermodynamics relates changes in the internal energy (or other cardinal energy function, depending on the conditions of the transfer) of the system to those two modes of energy transfer, as work, and as heat.
The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic processes, distinguishing two kinds of transfer of energy, as heat and as thermodynamic work.

### Internal energy

specific internal energyenergyheat energy
For a process in a closed (no transfer of matter) thermodynamic system, the first law of thermodynamics relates changes in the internal energy (or other cardinal energy function, depending on the conditions of the transfer) of the system to those two modes of energy transfer, as work, and as heat.
The internal energy of a system can be increased by introduction of matter, by heat, or by doing thermodynamic work on the system.

### Energy conversion efficiency

energy efficiencyefficiencyconversion efficiency
In the surroundings of a thermodynamic system, external to it, all the various mechanical and non-mechanical macroscopic forms of work can be converted into each other with no limitation in principle due to the laws of thermodynamics, so that the energy conversion efficiency can approach 100% in some cases; such conversion is required to be frictionless, and consequently adiabatic.

### Chemical thermodynamics

thermodynamicHistory of chemical thermodynamicsChemical energetics
PV work is an important topic in chemical thermodynamics.
Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of the laws of thermodynamics.

The statement that a process is reversible and adiabatic gives important information about the process but does not determine the path uniquely, because the path can include several slow goings backwards and forward in volume, as long as there is no transfer of energy as heat.
In an adiabatic process, energy is transferred to the surroundings only as work.

### Helmholtz free energy

Helmholtz energyfree energyHelmholtz
Two important cases are: in thermodynamic systems where the temperature and volume are held constant, the measure of useful work attainable is the Helmholtz free energy function; and in systems where the temperature and pressure are held constant, the measure of useful work attainable is the Gibbs free energy.
In thermodynamics, the Helmholtz free energy is a thermodynamic potential that measures the useful work obtainable from a closed thermodynamic system at a constant temperature and volume (isothermal, isochoric).

### Inexact differential

In the current mathematical notation, the differential \delta W is an inexact differential.
It is primarily used in calculations involving heat and work because they are path functions, not state functions.

### Exergy

exergeticaboveavailable energy
Under many practical situations this can be represented by the thermodynamic availability, or Exergy, function.
The term "exergy" was coined in 1956 by Zoran Rant (1904–1972) by using the Greek ex and ergon meaning "from work", but the concept was developed by J. Willard Gibbs in 1873.

### Calorimetry

calorimetriccalorimeterconstant pressure calorimetry
In experimental practice, heat transfer is often estimated calorimetrically, through change of temperature of a known quantity of calorimetric material substance.
The 'dynamics' contribution is based on the idea of work, which is not used in the above rules of calculation.

### Process function

process quantitiespath function
As for all kinds of work, in general, PV work is path-dependent and is, therefore, a thermodynamic process function.
Examples of path functions include work, heat and arc length.

### Gibbs free energy

Gibbs energyfree energyfree-energy
Two important cases are: in thermodynamic systems where the temperature and volume are held constant, the measure of useful work attainable is the Helmholtz free energy function; and in systems where the temperature and pressure are held constant, the measure of useful work attainable is the Gibbs free energy.
As a necessary condition for the reaction to occur at constant temperature and pressure, ΔG must be smaller than the non-PV (e.g. electrical) work, which is often equal to zero (hence ΔG must be negative).

### Microstate (statistical mechanics)

microstatesmicrostatemacrostates
Work is the energy transfer associated with an ordered, macroscopic action on the system.

### Macroscopic scale

macroscopicmacromacroscopically
In thermodynamics, work performed by a system is energy transferred by the system to its surroundings, by a mechanism through which the system can spontaneously exert macroscopic forces on its surroundings, where those forces, and their external effects, can be measured.

### State function

function of statestate variablesstate functions
For thermodynamic work, these externally measured quantities are exactly matched by values of or contributions to changes in macroscopic internal state variables of the system, which always occur in conjugate pairs, for example pressure and volume or magnetic flux density and magnetization.

### Joule heating

resistive heatingohmic heatingJoule's law
An example is Joule heating, because it occurs through friction as the electric current passes through the thermodynamic system.

### Work (physics)

workmechanical workwork-energy theorem
Thermodynamic work is a specialized version of the concept of work in physics.

### International System of Units

SISI unitsSI unit
In the SI system of measurement, work is measured in joules (symbol: J).

### Power (physics)

powermotive powerengine power
The rate at which work is performed is power.