In chemistry, Henry's law is a gas law that states that the amount of dissolved gas is proportional to its partial pressure in the gas phase. The proportionality factor is called the Henry's law constant. It was formulated by the English chemist William Henry, who studied the topic in the early 19th century. In his publication about the quantity of gases absorbed by water,[1] he described the results of his experiments: ..."water takes up, of gas condensed by one, two, or more additional atmospheres, a quantity which, ordinarily compressed, would be equal to twice, thrice, &c. the volume absorbed under the common pressure of the atmosphere." An example where Henry's law is at play is in the depthdependent dissolution of oxygen and nitrogen in the blood of underwater divers that changes during decompression, leading to decompression sickness. An everyday example is given by one's experience with carbonated soft drinks, which contain dissolved carbon dioxide. Before opening, the gas above the drink in its container is almost pure carbon dioxide, at a pressure higher than atmospheric pressure. After the bottle is opened, this gas escapes, moving the partial pressure of carbon dioxide above the liquid to be much lower, resulting in degassing as the dissolved carbon dioxide comes out of solution. Contents 1 Fundamental types and variants of Henry's law constants 1.1 Henry's law solubility constants H displaystyle H 1.1.1 Henry solubility defined via concentration ( H c p displaystyle H^ cp ) 1.1.2 The dimensionless Henry solubility H c c displaystyle H^ cc 1.1.3 Henry solubility defined via aqueousphase mixing ratio ( H x p displaystyle H^ xp ) 1.1.4 Henry solubility defined via molality ( H b p displaystyle H^ bp ) 1.1.5 The Bunsen coefficient α displaystyle alpha 1.1.6 The Kuenen coefficient S displaystyle S 1.2 Henry's law volatility constants K H displaystyle K_ text H 1.2.1 The Henry volatility defined via concentration ( K H p c displaystyle K_ text H ^ pc ) 1.2.2 The Henry volatility defined via aqueousphase mixing ratio ( K H p x displaystyle K_ text H ^ px ) 1.2.3 The dimensionless Henry volatility K H c c displaystyle K_ text H ^ cc 2 Values of Henry's law constants 3 Temperature dependence 4 Effective Henry's law constants Heff 5 Dependence on ionic strength (Sechenov equation) 6 Nonideal solutions 6.1 Solvent mixtures 7 Miscellaneous 7.1 In geochemistry 7.2 Comparison to Raoult's law 8 See also 9 References 10 External links Fundamental types and variants of Henry's law constants[edit] This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2016) (Learn how and when to remove this template message) There are many ways to define the proportionality constant of Henry's law, which can be subdivided into two fundamental types: One possibility is to put the aqueous phase into the numerator and the gaseous phase into the denominator ("aq/gas").[2] This results in the Henry's law solubility constant H displaystyle H . Its value increases with increased solubility. Alternatively, numerator and denominator can be switched ("gas/aq"), which results in the Henry's law volatility constant K H displaystyle K_ rm H . The value of K H displaystyle K_ rm H decreases with increased solubility. There are several variants of both fundamental types. This results from the multiplicity of quantities that can be chosen to describe the composition of the two phases. Typical choices for the aqueous phase are molar concentration ( c a displaystyle c_ rm a ), molality ( b displaystyle b ), and molar mixing ratio ( x displaystyle x ). For the gas phase, molar concentration ( c g displaystyle c_ rm g ) and partial pressure ( p displaystyle p ) are often used. It is not possible to use the gasphase mixing ratio ( y displaystyle y ) because at a given gasphase mixing ratio, the aqueousphase concentration c a displaystyle c_ rm a depends on the total pressure and thus the ratio y / c a displaystyle y/c_ rm a is not a constant.[3] To specify the exact variant of the Henry's law constant, two superscripts are used. They refer to the numerator and the denominator of the definition. For example, H c p displaystyle H^ cp refers to the Henry solubility defined as c / p displaystyle c/p . Henry's law solubility constants H displaystyle H [edit] This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2016) (Learn how and when to remove this template message) Henry solubility defined via concentration ( H c p displaystyle H^ cp )[edit] Atmospheric chemists often define the Henry solubility as H c p = c a / p displaystyle H^ cp =c_ text a /p .[2] Here c a displaystyle c_ text a is the concentration of a species in the aqueous phase, and p displaystyle p is the partial pressure of that species in the gas phase under
equilibrium conditions.[citation needed]
The
SI unit
H c p displaystyle H^ cp is mol/(m3 Pa); however, often the unit M/atm is used, since c a displaystyle c_ text a is usually expressed in M (1 M = 1 mol/dm3) and p displaystyle p in atm (1 atm = 101325 Pa).[citation needed] The dimensionless Henry solubility H c c displaystyle H^ cc [edit] The Henry solubility can also be expressed as the dimensionless ratio between the aqueousphase concentration c a displaystyle c_ text a of a species and its gasphase concentration c g displaystyle c_ text g : H c c = c a / c g displaystyle H^ cc =c_ text a /c_ text g .[2] For an ideal gas, the conversion is: H c c = H c p × R T displaystyle H^ cc =H^ cp times RT ,[2] where R displaystyle R is the gas constant and T displaystyle T is the temperature. Sometimes, this dimensionless constant is called the "waterair partitioning coefficient" K WA displaystyle K_ text WA .[4] It is closely related to the various, slightly different definitions of the "Ostwald coefficient" L displaystyle L , as discussed by Battino (1984).[5] Henry solubility defined via aqueousphase mixing ratio ( H x p displaystyle H^ xp )[edit] Another Henry's law solubility constant is H x p = x / p displaystyle H^ xp =x/p .[2] Here x displaystyle x is the molar mixing ratio in the aqueous phase. For a dilute aqueous solution the conversion between x displaystyle x and c a displaystyle c_ text a is: c a ≈ x ϱ H 2 O M H 2 O displaystyle c_ text a approx x frac varrho _ mathrm H_ 2 O M_ mathrm H_ 2 O ,[2] where ϱ H 2 O displaystyle varrho _ mathrm H_ 2 O is the density of water and M H 2 O displaystyle M_ mathrm H_ 2 O is the molar mass of water. Thus H x p ≈ M H 2 O ϱ H 2 O × H c p displaystyle H^ xp approx frac M_ mathrm H_ 2 O varrho _ mathrm H_ 2 O times H^ cp .[2] The
SI unit
H x p displaystyle H^ xp is Pa−1, although atm−1 is still frequently used.[2] Henry solubility defined via molality ( H b p displaystyle H^ bp )[edit] This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2016) (Learn how and when to remove this template message) It can be advantageous to describe the aqueous phase in terms of molality instead of concentration. The molality of a solution does not change with T displaystyle T , since it refers to the mass of the solvent. In contrast, the concentration c displaystyle c does change with T displaystyle T , since the density of a solution and thus its volume are temperaturedependent. Defining the aqueousphase composition via molality has the advantage that any temperature dependence of the Henry's law constant is a true solubility phenomenon and not introduced indirectly via a density change of the solution. Using molality, the Henry solubility can be defined as H b p = b / p . displaystyle H^ bp =b/p. Here b displaystyle b is used as the symbol for molality (instead of m displaystyle m ) to avoid confusion with the symbol m displaystyle m for mass. The
SI unit
H b p displaystyle H^ bp is mol/(kg Pa). There is no simple way to calculate H c p displaystyle H^ cp from H b p displaystyle H^ bp , since the conversion between concentration c a displaystyle c_ text a and molality b displaystyle b involves all solutes of a solution. For a solution with a total of n displaystyle n solutes with indices i = 1 , … , n displaystyle i=1,ldots ,n , the conversion is: c a = b ϱ 1 + ∑ i = 1 n b i M i , displaystyle c_ text a = frac bvarrho 1+sum _ i=1 ^ n b_ i M_ i , where ϱ displaystyle varrho is the density of the solution, and M i displaystyle M_ i are the molar masses. Here b displaystyle b is identical to one of the b i displaystyle b_ i in the denominator. If there is only one solute, the equation simplifies to c a = b ϱ 1 + b M . displaystyle c_ text a = frac bvarrho 1+bM . Henry's law is only valid for dilute solutions where b M ≪ 1 displaystyle bMll 1 and ϱ ≈ ϱ H 2 O displaystyle varrho approx varrho _ mathrm H_ 2 O . In this case the conversion reduces further to c a ≈ b ϱ H 2 O , displaystyle c_ text a approx bvarrho _ mathrm H_ 2 O , and thus H b p ≈ H c p / ϱ H 2 O . displaystyle H^ bp approx H^ cp /varrho _ mathrm H_ 2 O . The Bunsen coefficient α displaystyle alpha [edit] According to Sazonov and Shaw, the dimensionless Bunsen coefficient α displaystyle alpha is defined as "the volume of saturating gas, V1, reduced to T° = 273.15 K, p° = 1 bar, which is absorbed by unit volume V2* of pure solvent at the temperature of measurement and partial pressure of 1 bar."[6] If the gas is ideal, the pressure cancels out, and the conversion to H c p displaystyle H^ cp is simply H c p = α × 1 R T STP displaystyle H^ cp =alpha times frac 1 RT^ text STP ,[citation needed][original research?] with T STP displaystyle T^ text STP = 273.15 K. Note, that according to this definition, the conversion factor is not temperaturedependent.[citation needed] Independent of the temperature that the Bunsen coefficient refers to, 273.15 K is always used for the conversion.[citation needed] The Bunsen coefficient, which is named after Robert Bunsen, has been used mainly in the older literature.[citation needed] The Kuenen coefficient S displaystyle S [edit] According to Sazonov and Shaw, the Kuenen coefficient S displaystyle S is defined as "the volume of saturating gas V(g), reduced to T° = 273.15 K, p° = bar, which is dissolved by unit mass of pure solvent at the temperature of measurement and partial pressure 1 bar."[6] If the gas is ideal, the relation to H c p displaystyle H^ cp is H c p = S × ϱ R T STP displaystyle H^ cp =Stimes frac varrho RT^ text STP ,[citation needed][original research?] where ϱ displaystyle varrho is the density of the solvent, and T STP displaystyle T^ text STP = 273.15 K. The
SI unit
S displaystyle S is m3/kg.[6] The Kuenen coefficient, which is named after Johannes Kuenen, has been used mainly in the older literature, and IUPAC considers it to be obsolete.[7] Henry's law volatility constants K H displaystyle K_ text H [edit] This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2016) (Learn how and when to remove this template message) The Henry volatility defined via concentration ( K H p c displaystyle K_ text H ^ pc )[edit] A common way to define a Henry volatility is dividing the partial pressure by the aqueousphase concentration: K H p c = p / c a = 1 / H c p . displaystyle K_ text H ^ pc =p/c_ text a =1/H^ cp . The
SI unit
K H p c displaystyle K_ text H ^ pc is Pa m3/mol. The Henry volatility defined via aqueousphase mixing ratio ( K H p x displaystyle K_ text H ^ px )[edit] Another Henry volatility is K H p x = p / x = 1 / H x p . displaystyle K_ text H ^ px =p/x=1/H^ xp . The
SI unit
K H p x displaystyle K_ text H ^ px is Pa. However, atm is still frequently used. The dimensionless Henry volatility K H c c displaystyle K_ text H ^ cc [edit] The Henry volatility can also be expressed as the dimensionless ratio between the gasphase concentration c g displaystyle c_ text g of a species and its aqueousphase concentration c a displaystyle c_ text a : K H c c = c g / c a = 1 / H c c . displaystyle K_ text H ^ cc =c_ text g /c_ text a =1/H^ cc . In chemical engineering and environmental chemistry, this dimensionless constant is often called the air–water partitioning coefficient K AW displaystyle K_ text AW . Values of Henry's law constants[edit] A large compilation of Henry's law constants has been published by Sander (2015).[2] A few selected values are shown in the table below: Henry's law constants (gases in water at 298.15 K) equation: K H p c = p c aq displaystyle K_ text H ^ pc = frac p c_ text aq H c p = c aq p displaystyle H^ cp = frac c_ text aq p K H p x = p x displaystyle K_ text H ^ px = frac p x H c c = c aq c gas displaystyle H^ cc = frac c_ text aq c_ text gas unit: L ⋅ atm mol displaystyle frac text L cdot text atm text mol mol L ⋅ atm displaystyle frac text mol text L cdot text atm atm displaystyle text atm (dimensionless) O2 770 1.3×10−3 4.3×104 3.2×10−2 H2 1300 7.8×10−4 7.1×104 1.9×10−2 CO2 29 3.4×10−2 1.6×103 8.3×10−1 N2 1600 6.1×10−4 9.1×104 1.5×10−2 He 2700 3.7×10−4 1.5×105 9.1×10−3 Ne 2200 4.5×10−4 1.2×105 1.1×10−2 Ar 710 1.4×10−3 4.0×104 3.4×10−2 CO 1100 9.5×10−4 5.8×104 2.3×10−2 Temperature dependence[edit] This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2016) (Learn how and when to remove this template message) When the temperature of a system changes, the Henry constant also changes. The temperature dependence of equilibrium constants can generally be described with the van 't Hoff equation, which also applies to Henry's law constants: d ln H d ( 1 / T ) = − Δ sol H R , displaystyle frac mathrm d ln H mathrm d (1/T) = frac Delta _ text sol H R , where Δ sol H displaystyle Delta _ text sol H is the enthalpy of dissolution. Note that the letter H displaystyle H in the symbol Δ sol H displaystyle Delta _ text sol H refers to enthalpy and is not related to the letter H displaystyle H for Henry's law constants. Integrating the above equation and creating an expression based on H ∘ displaystyle H^ circ at the reference temperature T ∘ displaystyle T^ circ = 298.15 K yields: H ( T ) = H ∘ × exp [ − Δ sol H R ( 1 T − 1 T ∘ ) ] . displaystyle H(T)=H^ circ times exp displaystyle left[ frac Delta _ text sol H R left( frac 1 T  frac 1 T^ circ right)right]. The van 't Hoff equation in this form is only valid for a limited temperature range in which Δ sol H displaystyle Delta _ text sol H does not change much with temperature. The following table lists some temperature dependencies: Values of − Δ sol H / R displaystyle Delta _ text sol H/R (in K) O2 H2 CO2 N2 He Ne Ar CO 1700 500 2400 1300 230 490 1300 1300 Solubility of permanent gases usually decreases with increasing temperature at around room temperature. However, for aqueous solutions, the Henry's law solubility constant for many species goes through a minimum. For most permanent gases, the minimum is below 120 °C. Often, the smaller the gas molecule (and the lower the gas solubility in water), the lower the temperature of the maximum of the Henry's law constant. Thus, the maximum is at about 30 °C for helium, 92 to 93 °C for argon, nitrogen and oxygen, and 114 °C for xenon.[8] Effective Henry's law constants Heff[edit] This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2016) (Learn how and when to remove this template message) The Henry's law constants mentioned so far do not consider any chemical equilibria in the aqueous phase. This type is called the "intrinsic" (or "physical") Henry's law constant. For example, the intrinsic Henry's law solubility constant of formaldehyde can be defined as H cp = c ( H 2 CO ) p ( H 2 CO ) . displaystyle H^ ce cp = frac c( ce H2CO ) p( ce H2CO ) . In aqueous solution, methanal is almost completely hydrated: H 2 CO + H 2 O ↽ − − ⇀ H 2 C ( OH ) 2 displaystyle ce H2CO + H2O <=> H2C(OH)2 The total concentration of dissolved methanal is c tot = c ( H 2 CO ) + c ( H 2 C ( OH ) 2 ) . displaystyle c_ ce tot =c( ce H2CO )+c( ce H2C(OH)2 ). Taking this equilibrium into account, an effective Henry's law constant H eff displaystyle H_ ce eff can be defined as H eff = c tot p ( H 2 CO ) = c ( H 2 CO ) + c ( H 2 C ( OH ) 2 ) p ( H 2 CO ) . displaystyle H_ ce eff = frac c_ ce tot p( ce H2CO ) = frac c( ce H2CO )+c( ce H2C(OH)2 ) p( ce H2CO ) . For acids and bases, the effective Henry's law constant is not a useful quantity because it depends on the pH of the solution.[verification needed] In order to obtain a pHindependent constant, the product of the intrinsic Henry's law constant H cp displaystyle H^ ce cp and the acidity constant K A displaystyle K_ ce A is often used for strong acids like hydrochloric acid (HCl): H ′ = H cp × K A = c ( H + ) × c ( Cl − ) p ( HCl ) . displaystyle H'=H^ ce cp times K_ ce A = frac c( ce H+ )times c( ce Cl^ ) p( ce HCl ) . Although H ′ displaystyle H' is usually also called a Henry's law constant, it should be noted that it is a different quantity and it has different units than H cp displaystyle H^ ce cp . Dependence on ionic strength (Sechenov equation)[edit] This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2016) (Learn how and when to remove this template message) Values of Henry's law constants for aqueous solutions depend on the composition of the solution, i.e., on its ionic strength and on dissolved organics. In general, the solubility of a gas decreases with increasing salinity ("salting out"). However, a "salting in" effect has also been observed, for example for the effective Henry's law constant of glyoxal. The effect can be described with the Sechenov equation, named after the Russian physiologist Ivan Sechenov (sometimes the German transliteration "Setschenow" of the Cyrillic name Се́ченов is used). There are many alternative ways to define the Sechenov equation, depending on how the aqueousphase composition is described (based on concentration, molality, or molar fraction) and which variant of the Henry's law constant is used. Describing the solution in terms of molality is preferred because molality is invariant to temperature and to the addition of dry salt to the solution. Thus, the Sechenov equation can be written as log ( H 0 b p H b p ) = k s × b ( salt ) , displaystyle log left( frac H_ 0 ^ bp H^ bp right)=k_ text s times b( text salt ), where H 0 b p displaystyle H_ 0 ^ bp is the Henry's law constant in pure water, H b p displaystyle H^ bp is the Henry's law constant in the salt solution, k s displaystyle k_ text s is the molalitybased Sechenov constant, and b ( salt ) displaystyle b( text salt ) is the molality of the salt. Nonideal solutions[edit] Henry's law has been shown to apply to a wide range of solutes in the limit of "infinite dilution" (x → 0), including nonvolatile substances such as sucrose. In these cases, it is necessary to state the law in terms of chemical potentials. For a solute in an ideal dilute solution, the chemical potential depends only on the concentration. For nonideal solutions, the activity coefficients of the components must be taken into account: μ = μ c ∘ + R T ln γ c c c ∘ displaystyle mu =mu _ c ^ circ +RTln frac gamma _ c c c^ circ , where γ c = K H , c p ∗ displaystyle gamma _ c = frac K_ text H ,c p^ * for a volatile solute; c° = 1 mol/L. For nonideal solutions, the activity coefficient γc depends on the concentration and must be determined at the concentration of interest. The activity coefficient can also be obtained for nonvolatile solutes, where the vapor pressure of the pure substance is negligible, by using the GibbsDuhem relation: ∑ i n i d μ i = 0. displaystyle sum _ i n_ i dmu _ i =0. By measuring the change in vapor pressure (and hence chemical potential) of the solvent, the chemical potential of the solute can be deduced. The standard state for a dilute solution is also defined in terms of infinitedilution behavior. Although the standard concentration c° is taken to be 1 mol/l by convention, the standard state is a hypothetical solution of 1 mol/l in which the solute has its limiting infinitedilution properties. This has the effect that all nonideal behavior is described by the activity coefficient: the activity coefficient at 1 mol/l is not necessarily unity (and is frequently quite different from unity). All the relations above can also be expressed in terms of molalities b rather than concentrations, e.g.: μ = μ b ∘ + R T ln γ b b b ∘ , displaystyle mu =mu _ b ^ circ +RTln frac gamma _ b b b^ circ , where γ b = K H , b p ∗ displaystyle gamma _ b = frac K_ text H ,b p^ * for a volatile solute; b° = 1 mol/kg. The standard chemical potential μm°, the activity coefficient γm and the Henry's law constant KH,b all have different numerical values when molalities are used in place of concentrations. Solvent mixtures[edit] Henry law constant H2, M for a gas 2 in a mixture of solvents 1 and 3 is related to the constants for individual solvents H21 and H23: ln H 2 M = x 1 ln H 21 + x 2 ln H 23 − a 13 x 1 x 3 displaystyle ln H_ 2M =x_ 1 ln H_ 21 +x_ 2 ln H_ 23 a_ 13 x_ 1 x_ 3 where a13 is the interaction parameter of the solvents from Wohl expansion of the excess chemical potential of the ternary mixtures. Miscellaneous[edit] This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2016) (Learn how and when to remove this template message) In geochemistry[edit] In geochemistry, a version of Henry's law applies to the solubility of a noble gas in contact with silicate melt. One equation used is C melt / C gas = exp [ − β ( μ melt E − μ gas E ) ] , displaystyle C_ text melt /C_ text gas =exp left[beta (mu _ text melt ^ text E mu _ text gas ^ text E )right], where C is the number concentrations of the solute gas in the melt and gas phases, β = 1/kBT, an inverse temperature parameter (kB is the Boltzmann constant), µE is the excess chemical potentials of the solute gas in the two phases. Comparison to Raoult's law[edit] Henry's law is a limiting law that only applies for "sufficiently dilute" solutions. The range of concentrations in which it applies becomes narrower the more the system diverges from ideal behavior. Roughly speaking, that is the more chemically "different" the solute is from the solvent. For a dilute solution, the concentration of the solute is approximately proportional to its mole fraction x, and Henry's law can be written as p = K H x . displaystyle p=K_ text H x. This can be compared with Raoult's law: p = p ∗ x , displaystyle p=p^ * x, where p* is the vapor pressure of the pure component.
At first sight,
Raoult's law
Raoult's law: lim x → 1 ( p x ) = p ∗ . displaystyle lim _ xto 1 left( frac p x right)=p^ * . Henry's law: lim x → 0 ( p x ) = K H . displaystyle lim _ xto 0 left( frac p x right)=K_ text H .
Raoult's law
Pervaporation Partition coefficient Sieverts' law Graham's law Henry adsorption constant References[edit] ^ Henry, W. (1803). "Experiments on the quantity of gases absorbed by
water, at different temperatures, and under different pressures".
Phil. Trans. R. Soc. Lond. 93: 29–274.
doi:10.1098/rstl.1803.0004.
^ a b c d e f g h i Sander, R. (2015), "Compilation of Henry's law
constants (version 4.0) for water as solvent", Atmos. Chem. Phys., 15:
4399–4981, Bibcode:2015ACP....15.4399S,
doi:10.5194/acp1543992015
^ Sander, R. (1999). "Modeling atmospheric chemistry: Interactions
between gasphase species and liquid cloud/aerosol particles"
(review). Surv. Geophys. 20: 1–31. Retrieved 21 March 2016.
^ P.J. McCall; R.L. Swann; D.A. Laskowski, "6. Partition Models for
Equilibrium Distribution of Chemicals in Environmental Compartments",
in I.H. Suffet, Fate of Chemicals in the Environment
^ Battino, R.; Rettich, T. R.; Tominaga, T. (1984). "The solubility of
nitrogen and air in liquids". J. Phys. Chem. Ref. Data. 13:
563–600.
^ a b c Sazonov, V P & Shaw, DG (2006). "Introduction to the
Solubility Data Series: 1.5.2. §Physicochemical Quantities and Units,
A note on nomenclature, points 10 and 11". Introduction to IUPACNIST
Solubilities Database. nist.gov. Retrieved 21 March 2016. CS1
maint: Uses authors parameter (link)
^ Gamsjäger, H.; Lorimer, J. W.; Salomon, M.; Shaw, D. G.; Tomkins,
R. P. T. (2010). "The IUPACNIST Solubility Data Series: A guide to
preparation and use of compilations and evaluations (
IUPAC
External links[edit] EPA Online Tools for Site Assessment Calculation – Henry's law conversion v t e Chemical equilibria Concepts Acid dissociation constant
Binding constant
Binding selectivity
Buffer solution
Chemical equilibrium
Chemical stability
Chelation
Determination of equilibrium constants
Dissociation constant
Distribution coefficient
Dynamic equilibrium
Equilibrium chemistry
Equilibrium constant
Equilibrium unfolding
Equilibrium stage
Hammett acidity function
Henry's law
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