Table of thermodynamic equations

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Common thermodynamic equations and quantities in thermodynamics, using mathematical notation, are as follows:

Contents

Definitions

Many of the definitions below are also used in the thermodynamics of chemical reactions.

General basic quantities

Quantity (common name/s)(Common) symbol/sSI unitDimension
Number of moleculesN11
Amount of substancenmolN
Temperature TKΘ
Heat Energy Q, qJML2T−2
Latent heat QLJML2T−2

General derived quantities

Quantity (common name/s)(Common) symbol/sDefining equationSI unitDimension
Thermodynamic beta, inverse temperatureβJ−1T2M−1L−2
Thermodynamic temperature τ

JML2T−2
Entropy S

,

J⋅K−1ML2T−2Θ−1
Pressure P

PaML−1T−2
Internal Energy UJML2T−2
Enthalpy HJML2T−2
Partition Function Z11
Gibbs free energy GJML2T−2
Chemical potential (of component i in a mixture)μi

, where is not proportional to because depends on pressure. , where is proportional to (as long as the molar ratio composition of the system remains the same) because depends only on temperature and pressure and composition.

JML2T−2
Helmholtz free energy A, FJML2T−2
Landau potential, Landau free energy, Grand potential Ω, ΦGJML2T−2
Massieu potential, Helmholtz free entropy ΦJ⋅K−1ML2T−2Θ−1
Planck potential, Gibbs free entropy ΞJ⋅K−1ML2T−2Θ−1

Thermal properties of matter

Quantity (common name/s)(Common) symbol/sDefining equationSI unitDimension
General heat/thermal capacityCJ⋅K−1ML2T−2Θ−1
Heat capacity (isobaric)CpJ⋅K−1ML2T−2Θ−1
Specific heat capacity (isobaric)CmpJ⋅kg−1⋅K−1L2T−2Θ−1
Molar specific heat capacity (isobaric)CnpJ⋅K−1⋅mol−1ML2T−2Θ−1N−1
Heat capacity (isochoric/volumetric)CVJ⋅K−1ML2T−2Θ−1
Specific heat capacity (isochoric)CmVJ⋅kg−1⋅K−1L2T−2Θ−1
Molar specific heat capacity (isochoric)CnVJ⋅K⋅−1 mol−1ML2T−2Θ−1N−1
Specific latent heat LJ⋅kg−1L2T−2
Ratio of isobaric to isochoric heat capacity, heat capacity ratio, adiabatic index, Laplace coefficientγ11

Thermal transfer

Quantity (common name/s)(Common) symbol/sDefining equationSI unitDimension
Temperature gradient No standard symbolK⋅m−1ΘL−1
Thermal conduction rate, thermal current, thermal/heat flux, thermal power transferPWML2T−3
Thermal intensityIW⋅m−2MT−3
Thermal/heat flux density (vector analogue of thermal intensity above)qW⋅m−2MT−3

Equations

The equations in this article are classified by subject.

Thermodynamic processes

Physical situationEquations
Isentropic process (adiabatic and reversible)

For an ideal gas


Isothermal process

For an ideal gas

Isobaric process p1 = p2, p = constant

Isochoric process V1 = V2, V = constant

Free expansion
Work done by an expanding gasProcess

Net work done in cyclic processes

Kinetic theory

Ideal gas equations
Physical situationNomenclatureEquations
Ideal gas law

Pressure of an ideal gas
  • m = mass of one molecule
  • Mm = molar mass

Ideal gas

QuantityGeneral EquationIsobaric
Δp = 0
Isochoric
ΔV = 0
Isothermal
ΔT = 0
Adiabatic
Work
W

Heat Capacity
C
(as for real gas)
(for monatomic ideal gas)


(for diatomic ideal gas)


(for monatomic ideal gas)


(for diatomic ideal gas)

Internal Energy
ΔU






Enthalpy
ΔH
Entropy
Δs

[1]

Constant

Entropy

Statistical physics

Below are useful results from the Maxwell–Boltzmann distribution for an ideal gas, and the implications of the Entropy quantity. The distribution is valid for atoms or molecules constituting ideal gases.

Physical situationNomenclatureEquations
Maxwell–Boltzmann distribution
  • v = velocity of atom/molecule,
  • m = mass of each molecule (all molecules are identical in kinetic theory),
  • γ(p) = Lorentz factor as function of momentum (see below)
  • Ratio of thermal to rest mass-energy of each molecule:

K2 is the modified Bessel function of the second kind.

Non-relativistic speeds

Relativistic speeds (Maxwell–Jüttner distribution)

Entropy Logarithm of the density of states
  • Pi = probability of system in microstate i
  • Ω = total number of microstates

where:

Entropy change

Entropic force
Equipartition theorem df = degree of freedomAverage kinetic energy per degree of freedom

Internal energy

Corollaries of the non-relativistic Maxwell–Boltzmann distribution are below.

Physical situationNomenclatureEquations
Mean speed
Root mean square speed
Modal speed
Mean free path
  • σ = effective cross-section
  • n = volume density of number of target particles
  • = mean free path

Quasi-static and reversible processes

For quasi-static and reversible processes, the first law of thermodynamics is:

where δQ is the heat supplied to the system and δW is the work done by the system.

Thermodynamic potentials

The following energies are called the thermodynamic potentials,

NameSymbolFormulaNatural variables
Internal energy
Helmholtz free energy
Enthalpy
Gibbs free energy
Landau potential, or
grand potential
,

and the corresponding fundamental thermodynamic relations or "master equations" [2] are:

PotentialDifferential
Internal energy
Enthalpy
Helmholtz free energy
Gibbs free energy

Maxwell's relations

The four most common Maxwell's relations are:

Physical situationNomenclatureEquations
Thermodynamic potentials as functions of their natural variables

More relations include the following.

Other differential equations are:

NameHUG
Gibbs–Helmholtz equation

Quantum properties

where N is number of particles, h is that Planck constant, I is moment of inertia, and Z is the partition function, in various forms:

Degree of freedomPartition function
Translation
Vibration
Rotation

Thermal properties of matter

CoefficientsEquation
Joule-Thomson coefficient
Compressibility (constant temperature)
Coefficient of thermal expansion (constant pressure)
Heat capacity (constant pressure)
Heat capacity (constant volume)

Thermal transfer

Physical situationNomenclatureEquations
Net intensity emission/absorption
  • Texternal = external temperature (outside of system)
  • Tsystem = internal temperature (inside system)
  • ε = emissivity
Internal energy of a substance
  • CV = isovolumetric heat capacity of substance
  • ΔT = temperature change of substance
Meyer's equation
  • Cp = isobaric heat capacity
  • CV = isovolumetric heat capacity
  • n = amount of substance
Effective thermal conductivities
  • λi = thermal conductivity of substance i
  • λnet = equivalent thermal conductivity
Series

Parallel

Thermal efficiencies

Physical situationNomenclatureEquations
Thermodynamic engines
  • η = efficiency
  • W = work done by engine
  • QH = heat energy in higher temperature reservoir
  • QL = heat energy in lower temperature reservoir
  • TH = temperature of higher temp. reservoir
  • TL = temperature of lower temp. reservoir
Thermodynamic engine:

Carnot engine efficiency:

RefrigerationK = coefficient of refrigeration performanceRefrigeration performance

Carnot refrigeration performance

See also

References

  1. Keenan, Thermodynamics, Wiley, New York, 1947
  2. Physical chemistry, P.W. Atkins, Oxford University Press, 1978, ISBN   0 19 855148 7