Equation of state - Citizendia

For the use of this concept in cosmology, see Equation of state (cosmology). In cosmology, the equation of state of a Perfect fluid is characterized by a Dimensionless number w, equal to the ratio of its Pressure

In physics and thermodynamics, an equation of state is a relation between state variables. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " In Thermodynamics, state variables, state parameters or thermodynamic variables describe the momentary condition of a system. ^[1] More specifically, an equation of state is a thermodynamic equation describing the state of matter under a given set of physical conditions. For a quick reference table of these equations see Table of thermodynamic equations In Thermodynamics, there are a large number of equations It is a constitutive equation which provides a mathematical relationship between two or more state functions associated with the matter, such as its temperature, pressure, volume, or internal energy. In Structural analysis, constitutive relations connect applied stresses or Forces to strains or Deformations The constitutive relation In Thermodynamics, a state function, state quantity, or a function of state, is a property of a system that depends only on the current Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically In Thermodynamics, the internal energy of a Thermodynamic system, or a body with well-defined boundaries, denoted by U, or sometimes Equations of state are useful in describing the properties of fluids, mixtures of fluids, solids, and even the interior of stars. FLUID ( F ast L ight '''U'''ser '''I'''nterface D esigner is a graphical editor that is used to produce FLTK Source code A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth

1 Overview
2 Historical
3 Major equations of state
- 3.1 Classical ideal gas law
4 Cubic equations of state
5 Non-cubic equations of state
- 5.1 Dieterici equation of state
6 Virial equations of state
- 6.1 Virial equation of state
- 6.2 The BWRS equation of state
7 Other equations of state of interest
8 Equations of state for solids
9 See also
10 References
11 Bibliography
12 External links

Overview

The most prominent use of an equation of state is to predict the state of gases and liquids. One of the simplest equations of state for this purpose is the ideal gas law, which is roughly accurate for gases at low pressures and high temperatures. The ideal gas law is the Equation of state of a hypothetical Ideal gas, first stated by Benoît Paul Émile Clapeyron in 1834 However, this equation becomes increasingly inaccurate at higher pressures and lower temperatures, and fails to predict condensation from a gas to a liquid. Therefore, a number of much more accurate equations of state have been developed for gases and liquids. At present, there is no single equation of state that accurately predicts the properties of all substances under all conditions.

In addition to predicting the behavior of gases and liquids, there are also equations of state for predicting the volume of solids, including the transition of solids from one crystalline state to another. A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. There are equations that model the interior of stars, including neutron stars. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth A neutron star is a type of remnant that can result from the Gravitational collapse of a massive Star during a Type II, Type Ib or Type A related concept is the perfect fluid equation of state used in cosmology. In Physics, a perfect fluid is a Fluid that can be completely characterized by its rest frame Energy density &rho and isotropic Pressure In cosmology, the equation of state of a Perfect fluid is characterized by a Dimensionless number w, equal to the ratio of its Pressure

Historical

Boyle's law (1662)

Boyle's Law was perhaps the first expression of an equation of state. In 1662, the noted Irish physicist and chemist Robert Boyle performed a series of experiments employing a J-shaped glass tube, which was sealed on one end. Robert Boyle was a Natural philosopher, chemist physicist inventor and early Gentleman scientist, noted for his work in Physics and Chemistry Mercury was added to the tube, trapping a fixed quantity of air in the short, sealed end of the tube. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum Then the volume of gas was carefully measured as additional mercury was added to the tube. The pressure of the gas could be determined by the difference between the mercury level in the short end of the tube and that in the long, open end. Through these experiments, Boyle noted that the gas volume varied inversely with the pressure. In mathematical form, this can be stated as:

${\ pV = constant}$

The above relationship has also been attributed to Edme Mariotte and is sometimes referred to as Mariotte's law. Edme Mariotte (c 1620 - 12 May 1684) was a French Physicist and priest However, Mariotte's work was not published until 1676.

Charles's law or Law of Charles and Gay-Lussac (1787)

In 1787 the French physicist Jacques Charles found that oxygen, nitrogen, hydrogen, carbon dioxide, and air expand to the same extent over the same 80 kelvin interval. Jacques Alexandre César Charles ( November 12, 1746 – April 7, 1823) was a French inventor scientist mathematician and balloonist Later, in 1802, Joseph Louis Gay-Lussac published results of similar experiments, indicating a linear relationship between volume and temperature:

$\frac{V_1}{T_1} = \frac{V_2}{T_2}$

Dalton's law of partial pressures (1801)

Dalton's Law of Partial Pressure: The pressure of a mixture of gases is equal to the sum of the pressures of all of the constituent gases alone. Year 1802 ( MDCCCII) was a Common year starting on Friday of the Gregorian calendar or a Common year starting on Wednesday of the Joseph Louis Gay-Lussac (also Louis Joseph Gay-Lussac, December 6, 1778 – May 9, 1850) was a French chemist In Chemistry and Physics, Dalton's law (also called Dalton's law of partial pressures) states that the total Pressure exerted by a

Mathematically, this can be represented for n species as:

${\ P_{total} = p_1+p_2+\cdots+p_n}$

${\ or, P_{total} = \sum_{i=1}^n p_i}$

The ideal gas law (1834)

In 1834 Émile Clapeyron combined Boyle's Law and Charles' law into the first statement of the ideal gas law. Benoît Paul Émile Clapeyron (26 February 1799 - 28 January 1864 was a French Engineer and Physicist, one of the founders of Thermodynamics Initially the law was formulated as pV_m=R(T_C+267) (with temperature expressed in degrees Celsius). The Celsius Temperature scale was previously known as the centigrade scale. However, later work revealed that the number should actually be closer to 273. 2, and then the Celsius scale was defined with 0 °C = 273. 15 K, giving:

$\ pV_m = R (T_C+273.15)$

Van der Waals equation of state

In 1873, J. D. van der Waals introduced the first equation of state derived by the assumption of a finite volume occupied by the constituent molecules. The van der Waals equation is an Equation of state for a Fluid composed of particles that have a non-zero size and a pairwise attractive inter-particle Force ^[2] His new formula revolutionized the study of equations of state, and was most famously continued via the Redlich-Kwong equation of state and the Soave modification of Redlich-Kwong.

Major equations of state

For a given amount of substance contained in a system, the temperature, volume, and pressure are not independent quantities; they are connected by a relationship of the general form:

${\ f(p,V,T) = 0}$ .

In the following equations the variables are defined as follows. Any consistent set of units may be used, although SI units are preferred. Absolute temperature refers to use of the Kelvin (K) or Rankine (°R) temperature scales, with zero being absolute zero.

$\ p$ = pressure (absolute)

$\ V$ = volume

$\ n$ = number of moles of a substance

$\ V_m$ = $\frac{V}{n}$ = molar volume, the volume of 1 mole of gas or liquid

$\ T$ = absolute temperature

$\ R$ = ideal gas constant (8. The molar volume, symbol V m is the Volume occupied by one mole of a substance ( Chemical element or Chemical compound) Relationship with the Boltzmann constant The Boltzmann constant kB (often abbreviated k) may be used in place of the gas constant by working 314472 J/(mol·K))

$\ p_c$ = pressure at the critical point

$\ V_c$ = molar volume at the critical point

$\ T_c$ = absolute temperature at the critical point

Classical ideal gas law

The classical ideal gas law may be written:

${\ pV = nRT}$

The ideal gas law may also be expressed as follows

${\ p = \rho (\gamma-1)e}$

where $ρ$ is the density, $γ = C p / C v$ is the adiabatic index (ratio of specific heats), $e = C v T$ is the internal energy per unit mass (the "specific internal energy"), $C v$ is the specific heat at constant volume, and $C p$ is the specific heat at constant pressure. The ideal gas law is the Equation of state of a hypothetical Ideal gas, first stated by Benoît Paul Émile Clapeyron in 1834

Cubic equations of state

Van der Waals equation of state

The Van der Waals equation of state may be written:

${\left(p + \frac{a}{V_m^2}\right)\left(V_m-b\right) = RT}$ , note that

V m

is molar volume. The van der Waals equation is an Equation of state for a Fluid composed of particles that have a non-zero size and a pairwise attractive inter-particle Force

Where $a$ and $b$ are constants that depend on the specific material. They can be calculated from the critical properties as:

$a = 3p_c \,V_c^2$

$b = \frac{V_c}{3}$

Also written as

$a = \frac{27(R\,T_c)^2}{64p_c}$

$b = \frac{R\,T_c}{8p_c}$

Proposed in 1873, the van der Waals equation of state was one of the first to perform markedly better than the ideal gas law. The critical temperature, Tc of a material is the Temperature above which distinct Liquid and Gas phases do not exist In this landmark equation $a$ is called the attraction parameter and $b$ the repulsion parameter or the effective molecular volume. While the equation is definitely superior to the ideal gas law and does predict the formation of a liquid phase, the agreement with experimental data is limited for conditions where the liquid forms. While the van der Waals equation is commonly referenced in text-books and papers for historical reasons, it is now obsolete. Other modern equations of only slightly greater complexity are much more accurate.

The van der Waals equation may be considered as the ideal gas law, “improved” due to two independent reasons:

Molecules are thought as particles with volume, not material points. Thus $V$ cannot be too little, less than some constant. So we get ( $V - b$ ) instead of $V$ .
While ideal gas molecules do not interact, we consider molecules attracting others within a distance of several molecules' radii. It makes no effect inside the material, but surface molecules are attracted into the material from the surface. We see this as diminishing of pressure on the outer shell (which is used in the ideal gas law), so we write ( $p +$ something) instead of $p$ . To evaluate this ‘something’, let's examine an additional force acting on an element of gas surface. While the force acting on each surface molecule is ~ $ρ$ , the force acting on the whole element is ~ $ρ 2$ ~ $\frac{1}{V_m^2}$ .

Redlich-Kwong equation of state

${p = \frac{R\,T}{V_m-b} - \frac{a}{\sqrt{T}\,V_m\left(V_m+b\right)}}$

$a = \frac{0.42748\,R^2\,T_c^{\,2.5}}{p_c}$

$b = \frac{0.08662\,R\,T_c}{p_c}$

Introduced in 1949 the Redlich-Kwong equation of state was a considerable improvement over other equations of the time. It is still of interest primarily due to its relatively simple form. While superior to the van der Waals equation of state, it performs poorly with respect to the liquid phase and thus cannot be used for accurately calculating vapor-liquid equilibria. Vapor-liquid equilibrium, abbreviated as VLE by some is a condition where a Liquid and its Vapor (gas phase are in equilibrium with each other However, it can be used in conjunction with separate liquid-phase correlations for this purpose.

The Redlich-Kwong equation is adequate for calculation of gas phase properties when the ratio of the pressure to the critical pressure (reduced pressure) is less than about one-half of the ratio of the temperature to the critical temperature (reduced temperature):

$\frac{p}{p_c} < \frac{T}{2T_c}$

Soave modification of Redlich-Kwong

$p = \frac{R\,T}{V_m-b} - \frac{a\,\alpha}{V_m\left(V_m+b\right)}$

$a = \frac{0.42747\,R^2\,T_c^2}{P_c}$

$b = \frac{0.08664\,R\,T_c}{P_c}$

$\alpha = \left(1 + \left(0.48508 + 1.55171\,\omega - 0.15613\,\omega^2\right) \left(1-T_r^{\,0.5}\right)\right)^2$

$T_r = \frac{T}{T_c}$

Where ω is the acentric factor for the species. The critical temperature, Tc of a material is the Temperature above which distinct Liquid and Gas phases do not exist The critical temperature, Tc of a material is the Temperature above which distinct Liquid and Gas phases do not exist In Thermodynamics, the acentric factor \omega is a factor originally used by K

for hydrogen:

$\alpha = 1.202 \exp\left(-0.30288\,T_r\right)$

In 1972 Soave replaced the a/√(T) term of the Redlich-Kwong equation with a function α(T,ω) involving the temperature and the acentric factor. In Thermodynamics, the acentric factor \omega is a factor originally used by K The α function was devised to fit the vapor pressure data of hydrocarbons and the equation does fairly well for these materials.

Note especially that this replacement changes the definition of a slightly, as the $T c$ is now to the second power.

Peng-Robinson equation of state

$p=\frac{R\,T}{V_m-b} - \frac{a\,\alpha}{V_m^2+2bV_m-b^2}$

$a = \frac{0.45724\,R^2\,T_c^2}{p_c}$

$b = \frac{0.07780\,R\,T_c}{p_c}$

$\alpha = \left(1 + \left(0.37464 + 1.54226\,\omega - 0.26992\,\omega^2\right) \left(1-T_r^{\,0.5}\right)\right)^2$

$T_r = \frac{T}{T_c}$

In polynomial form:

$A = \frac{a\alpha P}{R^2 T^2}$

$B = \frac{bP}{RT}$

$Z^3 - (1-B)\ Z^2 + (A-3B^2-2B)\ Z -(AB-B^2-B^3) = 0 \,\!$

where, $ω$ is the acentric factor of the species and $R$ is the universal gas constant. In Thermodynamics, the acentric factor \omega is a factor originally used by K Relationship with the Boltzmann constant The Boltzmann constant kB (often abbreviated k) may be used in place of the gas constant by working

The Peng-Robinson equation was developed in 1976 in order to satisfy the following goals:^[3]

The parameters should be expressible in terms of the critical properties and the acentric factor. The critical temperature, Tc of a material is the Temperature above which distinct Liquid and Gas phases do not exist In Thermodynamics, the acentric factor \omega is a factor originally used by K
The model should provide reasonable accuracy near the critical point, particularly for calculations of the compressibility factor and liquid density. The compressibility factor ( Z) is a useful thermodynamic property for modifying the Ideal gas law to account for the Real gas behaviour
The mixing rules should not employ more than a single binary interaction parameter, which should be independent of temperature pressure and composition.
The equation should be applicable to all calculations of all fluid properties in natural gas processes.

For the most part the Peng-Robinson equation exhibits performance similar to the Soave equation, although it is generally superior in predicting the liquid densities of many materials, especially nonpolar ones. The departure functions of the Peng-Robinson equation are given on a separate article. In Thermodynamics, a departure function is defined for any thermodynamic property as the difference between the property as computed for an ideal gas and the property of the

Elliott, Suresh, Donohue equation of state

The Elliott, Suresh, and Donohue (ESD) equation of state was proposed in 1990 ^[4]. The equation seeks to correct a shortcoming in the Peng-Robinson EOS in that there was an inaccuracy in the van der Waals repulsive term. The EOS accounts for the effect of the shape of a non-polar molecule and can be extended to polymers with the addition of an extra term (not shown). The EOS itself was developed through modeling computer simulations and should capture the essential physics of the size, shape, and hydrogen bonding.

$\frac{pV_m}{RT}=Z=1+\frac{4\left\langle c\eta\right\rangle}{1-1.9\eta}-\frac{9.5\left\langle qY\eta\right\rangle}{1+1.7745\left\langle Y\eta\right\rangle}$

where:

c =

a “shape factor”

$\eta=b\cdot\rho$

$q=1+1.90476\cdot(c-1)$

$Y=\exp\left(\frac{\epsilon}{kT}\right)-1.0617$

Non-cubic equations of state

Dieterici equation of state

$\ p(V-b)=RTe^{-a/RTV}$

Where a is associated with the interaction between molecules and b takes into account the finite size of the molecules, similarly to the Van der Waals equation.

The reduced coordinates are:

$\ T_{c} = \frac{a}{4Rb}, \ p_{c} = \frac{a}{4e^{2}b^{2}}, \ V_{c} = 2b$

Virial equations of state

Virial equation of state

$\frac{pV_m}{RT} = 1 + \frac{B}{V_m} + \frac{C}{V_m^2} + \frac{D}{V_m^3} + \dots$

$B = -V_c \,$

$C = \frac{V_c^2}{3}$

Although usually not the most convenient equation of state, the virial equation is important because it can be derived directly from statistical mechanics. Statistical mechanics is the application of Probability theory, which includes mathematical tools for dealing with large populations to the field of Mechanics If appropriate assumptions are made about the mathematical form of intermolecular forces, theoretical expressions can be developed for each of the coefficients. Virial coefficients B_i appear as coefficients in the Virial expansion of the pressure of a Many-particle system in powers of the density In this case B corresponds to interactions between pairs of molecules, C to triplets, and so on. Accuracy can be increased indefinitely by considering higher order terms.

It can also be used to work out the Boyle Temperature (the temperature at which B = 0 and ideal gas laws apply) from a and b from the Van der Waals equation of state. If you use the value for B shown below;

$B = b - \frac{a}{RT}$

The BWRS equation of state

Main article: Benedict-Webb-Rubin

$p=\rho RT + \left(B_0 RT-A_0 - \frac{C_0}{T^2} + \frac{D_0}{T^3} - \frac{E_0}{T^4}\right) \rho^2 + \left(bRT-a-\frac{d}{T}\right) \rho^3 + \alpha\left(a+\frac{d}{T}\right) \rho^6 + \frac{c\rho^3}{T^2}\left(1 + \gamma\rho^2\right)\exp\left(-\gamma\rho^2\right)$

where

p = pressure

ρ = the molar density

Values of the various parameters for 15 substances can be found in:

K. The Benedict-Webb-Rubin equation ( BWR) is an Equation of state used in Fluid dynamics. E. Starling, Fluid Properties for Light Petroleum Systems. Gulf Publishing Company (1973).

Other equations of state of interest

Stiffened equation of state

When considering water under very high pressures (typical applications are underwater nuclear explosions, sonic shock lithotripsy, and sonoluminescence) the stiffened equation of state is often used:

$p=\rho(\gamma-1)e-\gamma p^0 \,$

where $e$ is the internal energy per unit mass, $γ$ is an empirically determined constant typically taken to be about 6. An underwater explosion, also known as an UNDEX, is an Explosion beneath the surface of water Sonoluminescence is the emission of short bursts of Light from imploding bubbles in a Liquid when excited by Sound. 1, and $p 0$ is another constant, representing the molecular attraction between water molecules. The magnitude of the correction is about 2 gigapascals (20000 atmospheres).

The equation is stated in this form because the speed of sound in water is given by $c 2 = γ(p + p 0) / ρ$ .

Thus water behaves as though it is an ideal gas that is already under about 20000 atmospheres (2 GPa) pressure, and explains why water is commonly assumed to be incompressible: when the external pressure changes from 1 atmosphere to 2 atmospheres (100 kPa to 200 kPa), the water behaves as an ideal gas would when changing from 20001 to 20002 atmospheres (2000. 1 MPa to 2000. 2 MPa).

This equation mispredicts the specific heat capacity of water but few alternatives are available for severely nonisentropic processes such as strong shocks. Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity

Ultrarelativistic equation of state

An ultrarelativistic fluid has equation of state

$p=c_s^2\mu$

where $p$ is the pressure, $μ$ is the energy density, and $c s$ is the speed of sound. Sound is a vibration that travels through an elastic medium as a Wave.

Ideal Bose equation of state

The equation of state for an ideal Bose gas is

$pV_m=RT~\frac{\textrm{Li}_{\alpha+1}(z)}{\zeta(\alpha)} \left(\frac{T}{T_c}\right)^\alpha$

where α is an exponent specific to the system (e. An ideal Bose gas is a quantum-mechanical version of a classical Ideal gas. g. in the absence of a potential field, α=3/2), z is exp(μ/kT) where μ is the chemical potential, Li is the polylogarithm, ζ is the Riemann zeta function, and T_c is the critical temperature at which a Bose-Einstein condensate begins to form. In Thermodynamics and Chemistry, chemical potential, symbolized by μ, is a term introduced by the American engineer chemist and mathematical The polylogarithm (also known as de Jonquière's function) is a Special function Li s ( z) that is defined by the sum In Mathematics, the Riemann zeta function, named after German mathematician Bernhard Riemann, is a function of great significance in A Bose–Einstein condensate (BEC is a State of matter of Bosons confined in an external Potential and cooled to Temperatures very near to

Equations of state for solids

Johnson Holmquist Equation of State

References

^ Perrot, Pierre (1998). In Solid mechanics, the Johnson-Holmquist Equation of state is used to model the behaviour of ceramics This articles outlines the historical development of the laws describing ideal gases In Thermodynamics, a departure function is defined for any thermodynamic property as the difference between the property as computed for an ideal gas and the property of the For more elaboration on these equations see Thermodynamic equations. A to Z of Thermodynamics. Oxford University Press. ISBN 0-19-856552-6.
^ van der Waals, J. D. (1873). On the Continuity of the Gaseous and Liquid States (doctoral dissertation). Universiteit Leiden.
^ "A New Two-Constant Equation of State" (1976). Industrial and Engineering Chemistry: Fundamentals 15: 59-64.
^ J. Richard Jr. Elliott, S. Jayaraman Suresh, Marc D. Donohue (1990). "A Simple Equation of State for Nonspherical and Associating Molecules". Ind. Eng. Chem. Res. 29: 1476-1485.

Bibliography

Elliot & Lira, (1999). Introductory Chemical Engineering Thermodynamics, Prentice Hall.

External links

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Contents

Overview

Historical

Boyle's law (1662)

Charles's law or Law of Charles and Gay-Lussac (1787)

Dalton's law of partial pressures (1801)

The ideal gas law (1834)

Van der Waals equation of state

Major equations of state

Classical ideal gas law

Cubic equations of state

Van der Waals equation of state

Redlich-Kwong equation of state

Soave modification of Redlich-Kwong

Peng-Robinson equation of state

Elliott, Suresh, Donohue equation of state

Non-cubic equations of state

Dieterici equation of state

Virial equations of state

Virial equation of state

The BWRS equation of state

Other equations of state of interest

Stiffened equation of state

Ultrarelativistic equation of state

Ideal Bose equation of state

Equations of state for solids

See also

References

Bibliography

External links