| Thermodynamics |
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Common thermodynamic equations and quantities in thermodynamics, using mathematical notation, are as follows:
Many of the definitions below are also used in the thermodynamics of chemical reactions.
| Quantity (common name/s) | (Common) symbol/s | SI unit | Dimension |
|---|---|---|---|
| Number of molecules | N | 1 | 1 |
| Amount of substance | n | mol | N |
| Temperature | T | K | Θ |
| Heat Energy | Q, q | J | ML2T−2 |
| Latent heat | QL | J | ML2T−2 |
| Quantity (common name/s) | (Common) symbol/s | Defining equation | SI unit | Dimension |
|---|---|---|---|---|
| Thermodynamic beta, inverse temperature | β | J−1 | T2M−1L−2 | |
| Thermodynamic temperature | τ | J | ML2T−2 | |
| Entropy | S | , | J⋅K−1 | ML2T−2Θ−1 |
| Pressure | P | Pa | ML−1T−2 | |
| Internal Energy | U | J | ML2T−2 | |
| Enthalpy | H | J | ML2T−2 | |
| Partition Function | Z | 1 | 1 | |
| Gibbs free energy | G | J | ML2T−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. | J | ML2T−2 |
| Helmholtz free energy | A, F | J | ML2T−2 | |
| Landau potential, Landau free energy, Grand potential | Ω, ΦG | J | ML2T−2 | |
| Massieu potential, Helmholtz free entropy | Φ | J⋅K−1 | ML2T−2Θ−1 | |
| Planck potential, Gibbs free entropy | Ξ | J⋅K−1 | ML2T−2Θ−1 | |
| Quantity (common name/s) | (Common) symbol/s | Defining equation | SI unit | Dimension |
|---|---|---|---|---|
| General heat/thermal capacity | C | J⋅K−1 | ML2T−2Θ−1 | |
| Heat capacity (isobaric) | Cp | J⋅K−1 | ML2T−2Θ−1 | |
| Specific heat capacity (isobaric) | Cmp | J⋅kg−1⋅K−1 | L2T−2Θ−1 | |
| Molar specific heat capacity (isobaric) | Cnp | J⋅K−1⋅mol−1 | ML2T−2Θ−1N−1 | |
| Heat capacity (isochoric/volumetric) | CV | J⋅K−1 | ML2T−2Θ−1 | |
| Specific heat capacity (isochoric) | CmV | J⋅kg−1⋅K−1 | L2T−2Θ−1 | |
| Molar specific heat capacity (isochoric) | CnV | J⋅K⋅−1 mol−1 | ML2T−2Θ−1N−1 | |
| Specific latent heat | L | J⋅kg−1 | L2T−2 | |
| Ratio of isobaric to isochoric heat capacity, heat capacity ratio, adiabatic index, Laplace coefficient | γ | 1 | 1 | |
| Quantity (common name/s) | (Common) symbol/s | Defining equation | SI unit | Dimension |
|---|---|---|---|---|
| Temperature gradient | No standard symbol | K⋅m−1 | ΘL−1 | |
| Thermal conduction rate, thermal current, thermal/heat flux, thermal power transfer | P | W | ML2T−3 | |
| Thermal intensity | I | W⋅m−2 | MT−3 | |
| Thermal/heat flux density (vector analogue of thermal intensity above) | q | W⋅m−2 | MT−3 | |
The equations in this article are classified by subject.
| Physical situation | Equations |
|---|---|
| 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 gas | Process Net work done in cyclic processes |
| Physical situation | Nomenclature | Equations |
|---|---|---|
| Ideal gas law |
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| Pressure of an ideal gas |
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| Quantity | General Equation | Isobaric Δp = 0 | Isochoric ΔV = 0 | Isothermal ΔT = 0 | Adiabatic |
|---|---|---|---|---|---|
| Work W | |||||
| Heat Capacity C | (as for real gas) | (for monatomic ideal gas)
| (for monatomic ideal gas)
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| Internal Energy ΔU | |||||
| Enthalpy ΔH | |||||
| Entropy Δs | [1] | ||||
| Constant |
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 situation | Nomenclature | Equations |
|---|---|---|
| Maxwell–Boltzmann distribution |
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 |
| where: |
| Entropy change | ||
| Entropic force | ||
| Equipartition theorem | df = degree of freedom | Average kinetic energy per degree of freedom Internal energy |
Corollaries of the non-relativistic Maxwell–Boltzmann distribution are below.
| Physical situation | Nomenclature | Equations |
|---|---|---|
| Mean speed | ||
| Root mean square speed | ||
| Modal speed | ||
| Mean free path |
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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.
The following energies are called the thermodynamic potentials,
| Name | Symbol | Formula | Natural 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:
| Potential | Differential |
|---|---|
| Internal energy | |
| Enthalpy | |
| Helmholtz free energy | |
| Gibbs free energy | |
The four most common Maxwell's relations are:
| Physical situation | Nomenclature | Equations |
|---|---|---|
| Thermodynamic potentials as functions of their natural variables | ||
More relations include the following.
Other differential equations are:
| Name | H | U | G |
|---|---|---|---|
| Gibbs–Helmholtz equation | |||
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 freedom | Partition function |
|---|---|
| Translation | |
| Vibration | |
| Rotation |
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| Coefficients | Equation |
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| Joule-Thomson coefficient | |
| Compressibility (constant temperature) | |
| Coefficient of thermal expansion (constant pressure) | |
| Heat capacity (constant pressure) | |
| Heat capacity (constant volume) | |
| Derivation of heat capacity (constant pressure) |
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Since |
| Derivation of heat capacity (constant volume) |
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Since (where δWrev is the work done by the system), |
| Physical situation | Nomenclature | Equations |
|---|---|---|
| Net intensity emission/absorption |
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| Internal energy of a substance |
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| Meyer's equation |
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| Effective thermal conductivities |
| Series Parallel |
| Physical situation | Nomenclature | Equations |
|---|---|---|
| Thermodynamic engines |
| Thermodynamic engine: Carnot engine efficiency: |
| Refrigeration | K = coefficient of refrigeration performance | Refrigeration performance Carnot refrigeration performance |