Standard enthalpy of formation
Inchemistryandthermodynamics,thestandard enthalpy of formationorstandard heat of formationof acompoundis the change ofenthalpyduring the formation of 1moleof the substance from its constituentelements in their reference state,with all substances in theirstandard states.The standardpressurevaluep⦵= 105Pa(= 100 kPa = 1bar)is recommended byIUPAC,although prior to 1982 the value 1.00atm(101.325 kPa) was used.[1]There is no standard temperature. Its symbol is ΔfH⦵.The superscriptPlimsollon this symbol indicates that the process has occurred under standard conditions at the specified temperature (usually 25 °C or 298.15 K).
Standard states are defined for various types of substances. For a gas, it is the hypothetical state the gas would assume if it obeyed theideal gas equationat a pressure of 1 bar. For a gaseous or solidsolutepresent in a dilutedideal solution,the standard state is the hypothetical state of concentration of the solute of exactly one mole per liter (1M) at a pressure of 1 bar extrapolated from infinite dilution. For a pure substance or asolventin a condensed state (a liquid or a solid) the standard state is the pure liquid or solid under a pressure of 1 bar.
For elements that have multipleallotropes,the reference state usually is chosen to be the form in which the element is most stable under 1 bar of pressure. One exception isphosphorus,for which the most stable form at 1 bar isblack phosphorus,but white phosphorus is chosen as the standard reference state for zero enthalpy of formation.[2]
For example, the standard enthalpy of formation ofcarbon dioxideis the enthalpy of the following reaction under the above conditions:
All elements are written in their standard states, and one mole of product is formed. This is true for all enthalpies of formation.
The standard enthalpy of formation is measured in units of energy per amount of substance, usually stated inkilojoule per mole(kJ mol−1), but also inkilocalorie per mole,jouleper mole or kilocalorie pergram(any combination of these units conforming to the energy per mass or amount guideline).
All elements in their reference states (oxygengas, solidcarbonin the form ofgraphite,etc.) have a standard enthalpy of formation of zero, as there is no change involved in their formation.
The formation reaction is a constant pressure and constant temperature process. Since the pressure of the standard formation reaction is fixed at 1 bar, the standard formation enthalpy or reaction heat is a function of temperature. For tabulation purposes, standard formation enthalpies are all given at a single temperature: 298 K, represented by the symbolΔfH⦵
298 K.
Hess's law
[edit]For many substances, the formation reaction may be considered as the sum of a number of simpler reactions, either real or fictitious. Theenthalpy of reactioncan then be analyzed by applyingHess's Law,which states that thesumof the enthalpy changes for a number of individual reaction steps equals the enthalpy change of the overall reaction. This is true because enthalpy is astate function,whose value for an overall process depends only on the initial and final states and not on any intermediate states. Examples are given in the following sections.
Ionic compounds: Born–Haber cycle
[edit]For ionic compounds, the standard enthalpy of formation is equivalent to the sum of several terms included in theBorn–Haber cycle.For example, the formation oflithium fluoride,
may be considered as the sum of several steps, each with its own enthalpy (or energy, approximately):
- Hsub,thestandard enthalpy of atomization(orsublimation) of solid lithium.
- IELi,thefirst ionization energyof gaseous lithium.
- B(F–F),the standardenthalpy of atomization(or bond energy) of fluorine gas.
- EAF,theelectron affinityof a fluorine atom.
- UL,thelattice energyof lithium fluoride.
The sum of these enthalpies give the standard enthalpy of formation (ΔfH) of lithium fluoride:
In practice, the enthalpy of formation of lithium fluoride can be determined experimentally, but the lattice energy cannot be measured directly. The equation is therefore rearranged to evaluate the lattice energy:[3]
Organic compounds
[edit]The formation reactions for most organic compounds are hypothetical. For instance, carbon and hydrogen will not directly react to formmethane(CH4), so that the standard enthalpy of formation cannot be measured directly. However thestandard enthalpy of combustionis readily measurable usingbomb calorimetry.The standard enthalpy of formation is then determined usingHess's law.The combustion of methane:
is equivalent to the sum of the hypothetical decomposition into elements followed by the combustion of the elements to formcarbon dioxide(CO2) and water (H2O):
Applying Hess's law,
Solving for the standard of enthalpy of formation,
The value ofis determined to be −74.8 kJ/mol. The negative sign shows that the reaction, if it were to proceed, would beexothermic;that is, methane is enthalpically more stable than hydrogen gas and carbon.
It is possible to predict heats of formation for simpleunstrainedorganic compounds with theheat of formation group additivitymethod.
Use in calculation for other reactions
[edit]Thestandard enthalpy change of any reactioncan be calculated from the standard enthalpies of formation of reactants and products using Hess's law. A given reaction is considered as the decomposition of all reactants into elements in their standard states, followed by the formation of all products. The heat of reaction is thenminusthe sum of the standard enthalpies of formation of the reactants (each being multiplied by its respective stoichiometric coefficient,ν)plusthe sum of the standard enthalpies of formation of the products (each also multiplied by its respective stoichiometric coefficient), as shown in the equation below:[4]
If the standard enthalpy of the products is less than the standard enthalpy of the reactants, the standard enthalpy of reaction is negative. This implies that the reaction is exothermic. The converse is also true; the standard enthalpy of reaction is positive for an endothermic reaction. This calculation has a tacit assumption ofideal solutionbetween reactants and products where theenthalpy of mi xingis zero.
For example, for the combustion of methane,:
Howeveris an element in its standard state, so that,and the heat of reaction is simplified to
which is the equation in the previous section for the enthalpy of combustion.
Key concepts for enthalpy calculations
[edit]- When a reaction is reversed, the magnitude of ΔHstays the same, but the sign changes.
- When the balanced equation for a reaction is multiplied by an integer, the corresponding value of ΔHmust be multiplied by that integer as well.
- The change in enthalpy for a reaction can be calculated from the enthalpies of formation of the reactants and the products
- Elements in their standard states make no contribution to the enthalpy calculations for the reaction, since the enthalpy of an element in its standard state is zero.Allotropesof an element other than the standard state generally have non-zero standard enthalpies of formation.
Examples: standard enthalpies of formation at 25 °C
[edit]Thermochemical properties of selected substances at 298.15 K and 1 atm
Inorganic substances
[edit]Species | Phase | Chemical formula | ΔfH⦵/(kJ/mol) |
---|---|---|---|
Aluminium | Solid | Al | 0 |
Aluminium chloride | Solid | AlCl3 | −705.63 |
Aluminium oxide | Solid | Al2O3 | −1675.5 |
Aluminium hydroxide | Solid | Al(OH)3 | −1277 |
Aluminium sulphate | Solid | Al2(SO4)3 | −3440 |
Barium chloride | Solid | BaCl2 | −858.6 |
Barium carbonate | Solid | BaCO3 | −1216 |
Barium hydroxide | Solid | Ba(OH)2 | −944.7 |
Barium oxide | Solid | BaO | −548.1 |
Barium sulfate | Solid | BaSO4 | −1473.3 |
Beryllium | Solid | Be | 0 |
Beryllium hydroxide | Solid | Be(OH)2 | −903 |
Beryllium oxide | Solid | BeO | −609.4 |
Boron trichloride | Solid | BCl3 | −402.96 |
Bromine | Liquid | Br2 | 0 |
Bromide ion | Aqueous | Br− | −121 |
Bromine | Gas | Br | 111.884 |
Bromine | Gas | Br2 | 30.91 |
Bromine trifluoride | Gas | BrF3 | −255.60 |
Hydrogen bromide | Gas | HBr | −36.29 |
Cadmium | Solid | Cd | 0 |
Cadmium oxide | Solid | CdO | −258 |
Cadmium hydroxide | Solid | Cd(OH)2 | −561 |
Cadmium sulfide | Solid | CdS | −162 |
Cadmium sulfate | Solid | CdSO4 | −935 |
Caesium | Solid | Cs | 0 |
Caesium | Gas | Cs | 76.50 |
Caesium | Liquid | Cs | 2.09 |
Caesium(I) ion | Gas | Cs+ | 457.964 |
Caesium chloride | Solid | CsCl | −443.04 |
Calcium | Solid | Ca | 0 |
Calcium | Gas | Ca | 178.2 |
Calcium(II) ion | Gas | Ca2+ | 1925.90 |
Calcium(II) ion | Aqueous | Ca2+ | −542.7 |
Calcium carbide | Solid | CaC2 | −59.8 |
Calcium carbonate(Calcite) | Solid | CaCO3 | −1206.9 |
Calcium chloride | Solid | CaCl2 | −795.8 |
Calcium chloride | Aqueous | CaCl2 | −877.3 |
Calcium phosphate | Solid | Ca3(PO4)2 | −4132 |
Calcium fluoride | Solid | CaF2 | −1219.6 |
Calcium hydride | Solid | CaH2 | −186.2 |
Calcium hydroxide | Solid | Ca(OH)2 | −986.09 |
Calcium hydroxide | Aqueous | Ca(OH)2 | −1002.82 |
Calcium oxide | Solid | CaO | −635.09 |
Calcium sulfate | Solid | CaSO4 | −1434.52 |
Calcium sulfide | Solid | CaS | −482.4 |
Wollastonite | Solid | CaSiO3 | −1630 |
Carbon(Graphite) | Solid | C | 0 |
Carbon(Diamond) | Solid | C | 1.9 |
Carbon | Gas | C | 716.67 |
Carbon dioxide | Gas | CO2 | −393.509 |
Carbon disulfide | Liquid | CS2 | 89.41 |
Carbon disulfide | Gas | CS2 | 116.7 |
Carbon monoxide | Gas | CO | −110.525 |
Carbonyl chloride(Phosgene) | Gas | COCl2 | −218.8 |
Carbon dioxide (un–ionized) | Aqueous | CO2(aq) | −419.26 |
Bicarbonateion | Aqueous | HCO3– | −689.93 |
Carbonateion | Aqueous | CO32– | −675.23 |
Monatomic chlorine | Gas | Cl | 121.7 |
Chlorideion | Aqueous | Cl− | −167.2 |
Chlorine | Gas | Cl2 | 0 |
Chromium | Solid | Cr | 0 |
Copper | Solid | Cu | 0 |
Copper(II) bromide | Solid | CuBr2 | −138.490 |
Copper(II) chloride | Solid | CuCl2 | −217.986 |
Copper(II) oxide | Solid | CuO | −155.2 |
Copper(II) sulfate | Aqueous | CuSO4 | −769.98 |
Fluorine | Gas | F2 | 0 |
Monatomic hydrogen | Gas | H | 218 |
Hydrogen | Gas | H2 | 0 |
Water | Gas | H2O | −241.818 |
Water | Liquid | H2O | −285.8 |
Hydrogen ion | Aqueous | H+ | 0 |
Hydroxide ion | Aqueous | OH− | −230 |
Hydrogen peroxide | Liquid | H2O2 | −187.8 |
Phosphoric acid | Liquid | H3PO4 | −1288 |
Hydrogen cyanide | Gas | HCN | 130.5 |
Hydrogen bromide | Liquid | HBr | −36.3 |
Hydrogen chloride | Gas | HCl | −92.30 |
Hydrogen chloride | Aqueous | HCl | −167.2 |
Hydrogen fluoride | Gas | HF | −273.3 |
Hydrogen iodide | Gas | HI | 26.5 |
Iodine | Solid | I2 | 0 |
Iodine | Gas | I2 | 62.438 |
Iodine | Aqueous | I2 | 23 |
Iodideion | Aqueous | I− | −55 |
Iron | Solid | Fe | 0 |
Iron carbide (Cementite) | Solid | Fe3C | 5.4 |
Iron(II) carbonate (Siderite) | Solid | FeCO3 | −750.6 |
Iron(III) chloride | Solid | FeCl3 | −399.4 |
Iron(II) oxide(Wüstite) | Solid | FeO | −272 |
Iron(II,III) oxide(Magnetite) | Solid | Fe3O4 | −1118.4 |
Iron(III) oxide(Hematite) | Solid | Fe2O3 | −824.2 |
Iron(II) sulfate | Solid | FeSO4 | −929 |
Iron(III) sulfate | Solid | Fe2(SO4)3 | −2583 |
Iron(II) sulfide | Solid | FeS | −102 |
Pyrite | Solid | FeS2 | −178 |
Lead | Solid | Pb | 0 |
Lead dioxide | Solid | PbO2 | −277 |
Lead sulfide | Solid | PbS | −100 |
Lead sulfate | Solid | PbSO4 | −920 |
Lead(II) nitrate | Solid | Pb(NO3)2 | −452 |
Lead(II) sulfate | Solid | PbSO4 | −920 |
Lithium fluoride | Solid | LiF | −616.93 |
Magnesium | Solid | Mg | 0 |
Magnesium ion | Aqueous | Mg2+ | −466.85 |
Magnesium carbonate | Solid | MgCO3 | −1095.797 |
Magnesium chloride | Solid | MgCl2 | −641.8 |
Magnesium hydroxide | Solid | Mg(OH)2 | −924.54 |
Magnesium hydroxide | Aqueous | Mg(OH)2 | −926.8 |
Magnesium oxide | Solid | MgO | −601.6 |
Magnesium sulfate | Solid | MgSO4 | −1278.2 |
Manganese | Solid | Mn | 0 |
Manganese(II) oxide | Solid | MnO | −384.9 |
Manganese(IV) oxide | Solid | MnO2 | −519.7 |
Manganese(III) oxide | Solid | Mn2O3 | −971 |
Manganese(II,III) oxide | Solid | Mn3O4 | −1387 |
Permanganate | Aqueous | MnO− 4 |
−543 |
Mercury(II) oxide(red) | Solid | HgO | −90.83 |
Mercury sulfide(red,cinnabar) | Solid | HgS | −58.2 |
Nitrogen | Gas | N2 | 0 |
Ammonia(ammonium hydroxide) | Aqueous | NH3(NH4OH) | −80.8 |
Ammonia | Gas | NH3 | −46.1 |
Ammonium nitrate | Solid | NH4NO3 | −365.6 |
Ammonium chloride | Solid | NH4Cl | −314.55 |
Nitrogen dioxide | Gas | NO2 | 33.2 |
Hydrazine | Gas | N2H4 | 95.4 |
Hydrazine | Liquid | N2H4 | 50.6 |
Nitrous oxide | Gas | N2O | 82.05 |
Nitric oxide | Gas | NO | 90.29 |
Dinitrogen tetroxide | Gas | N2O4 | 9.16 |
Dinitrogen pentoxide | Solid | N2O5 | −43.1 |
Dinitrogen pentoxide | Gas | N2O5 | 11.3 |
Nitric acid | Aqueous | HNO3 | −207 |
Monatomic oxygen | Gas | O | 249 |
Oxygen | Gas | O2 | 0 |
Ozone | Gas | O3 | 143 |
White phosphorus | Solid | P4 | 0 |
Red phosphorus | Solid | P | −17.4[5] |
Black phosphorus | Solid | P | −39.3[5] |
Phosphorus trichloride | Liquid | PCl3 | −319.7 |
Phosphorus trichloride | Gas | PCl3 | −278 |
Phosphorus pentachloride | Solid | PCl5 | −440 |
Phosphorus pentachloride | Gas | PCl5 | −321 |
Phosphorus pentoxide | Solid | P2O5 | −1505.5[6] |
Potassium bromide | Solid | KBr | −392.2 |
Potassium carbonate | Solid | K2CO3 | −1150 |
Potassium chlorate | Solid | KClO3 | −391.4 |
Potassium chloride | Solid | KCl | −436.68 |
Potassium fluoride | Solid | KF | −562.6 |
Potassium oxide | Solid | K2O | −363 |
Potassium nitrate | Solid | KNO3 | −494.5 |
Potassium perchlorate | Solid | KClO4 | −430.12 |
Silicon | Gas | Si | 368.2 |
Silicon carbide | Solid | SiC | −74.4,[7]−71.5[8] |
Silicon tetrachloride | Liquid | SiCl4 | −640.1 |
Silica(Quartz) | Solid | SiO2 | −910.86 |
Silver bromide | Solid | AgBr | −99.5 |
Silver chloride | Solid | AgCl | −127.01 |
Silver iodide | Solid | AgI | −62.4 |
Silver oxide | Solid | Ag2O | −31.1 |
Silver sulfide | Solid | Ag2S | −31.8 |
Sodium | Solid | Na | 0 |
Sodium | Gas | Na | 107.5 |
Sodium bicarbonate | Solid | NaHCO3 | −950.8 |
Sodium carbonate | Solid | Na2CO3 | −1130.77 |
Sodium chloride | Aqueous | NaCl | −407.27 |
Sodium chloride | Solid | NaCl | −411.12 |
Sodium chloride | Liquid | NaCl | −385.92 |
Sodium chloride | Gas | NaCl | −181.42 |
Sodium chlorate | Solid | NaClO3 | −365.4 |
Sodium fluoride | Solid | NaF | −569.0 |
Sodium hydroxide | Aqueous | NaOH | −469.15 |
Sodium hydroxide | Solid | NaOH | −425.93 |
Sodium hypochlorite | Solid | NaOCl | −347.1 |
Sodium nitrate | Aqueous | NaNO3 | −446.2 |
Sodium nitrate | Solid | NaNO3 | −424.8 |
Sodium oxide | Solid | Na2O | −414.2 |
Sulfur (monoclinic) | Solid | S8 | 0.3 |
Sulfur (rhombic) | Solid | S8 | 0 |
Hydrogen sulfide | Gas | H2S | −20.63 |
Sulfur dioxide | Gas | SO2 | −296.84 |
Sulfur trioxide | Gas | SO3 | −395.7 |
Sulfuric acid | Liquid | H2SO4 | −814 |
Titanium | Gas | Ti | 468 |
Titanium tetrachloride | Gas | TiCl4 | −763.2 |
Titanium tetrachloride | Liquid | TiCl4 | −804.2 |
Titanium dioxide | Solid | TiO2 | −944.7 |
Zinc | Gas | Zn | 130.7 |
Zinc chloride | Solid | ZnCl2 | −415.1 |
Zinc oxide | Solid | ZnO | −348.0 |
Zinc sulfate | Solid | ZnSO4 | −980.14 |
Aliphatic hydrocarbons
[edit]Formula | Name | ΔfH⦵/(kcal/mol) | ΔfH⦵/(kJ/mol) |
---|---|---|---|
Straight-chain | |||
CH4 | Methane | −17.9 | −74.9 |
C2H6 | Ethane | −20.0 | −83.7 |
C2H4 | Ethylene | 12.5 | 52.5 |
C2H2 | Acetylene | 54.2 | 226.8 |
C3H8 | Propane | −25.0 | −104.6 |
C4H10 | n-Butane | −30.0 | −125.5 |
C5H12 | n-Pentane | −35.1 | −146.9 |
C6H14 | n-Hexane | −40.0 | −167.4 |
C7H16 | n-Heptane | −44.9 | −187.9 |
C8H18 | n-Octane | −49.8 | −208.4 |
C9H20 | n-Nonane | −54.8 | −229.3 |
C10H22 | n-Decane | −59.6 | −249.4 |
C4Alkane branched isomers | |||
C4H10 | Isobutane(methylpropane) | −32.1 | −134.3 |
C5Alkane branched isomers | |||
C5H12 | Neopentane(dimethylpropane) | −40.1 | −167.8 |
C5H12 | Isopentane(methylbutane) | −36.9 | −154.4 |
C6Alkane branched isomers | |||
C6H14 | 2,2-Dimethylbutane | −44.5 | −186.2 |
C6H14 | 2,3-Dimethylbutane | −42.5 | −177.8 |
C6H14 | 2-Methylpentane(isohexane) | −41.8 | −174.9 |
C6H14 | 3-Methylpentane | −41.1 | −172.0 |
C7Alkane branched isomers | |||
C7H16 | 2,2-Dimethylpentane | −49.2 | −205.9 |
C7H16 | 2,2,3-Trimethylbutane | −49.0 | −205.0 |
C7H16 | 3,3-Dimethylpentane | −48.1 | −201.3 |
C7H16 | 2,3-Dimethylpentane | −47.3 | −197.9 |
C7H16 | 2,4-Dimethylpentane | −48.2 | −201.7 |
C7H16 | 2-Methylhexane | −46.5 | −194.6 |
C7H16 | 3-Methylhexane | −45.7 | −191.2 |
C7H16 | 3-Ethylpentane | −45.3 | −189.5 |
C8Alkane branched isomers | |||
C8H18 | 2,3-Dimethylhexane | −55.1 | −230.5 |
C8H18 | 2,2,3,3-Tetramethylbutane | −53.9 | −225.5 |
C8H18 | 2,2-Dimethylhexane | −53.7 | −224.7 |
C8H18 | 2,2,4-Trimethylpentane(isooctane) | −53.5 | −223.8 |
C8H18 | 2,5-Dimethylhexane | −53.2 | −222.6 |
C8H18 | 2,2,3-Trimethylpentane | −52.6 | −220.1 |
C8H18 | 3,3-Dimethylhexane | −52.6 | −220.1 |
C8H18 | 2,4-Dimethylhexane | −52.4 | −219.2 |
C8H18 | 2,3,4-Trimethylpentane | −51.9 | −217.1 |
C8H18 | 2,3,3-Trimethylpentane | −51.7 | −216.3 |
C8H18 | 2-Methylheptane | −51.5 | −215.5 |
C8H18 | 3-Ethyl-3-Methylpentane | −51.4 | −215.1 |
C8H18 | 3,4-Dimethylhexane | −50.9 | −213.0 |
C8H18 | 3-Ethyl-2-Methylpentane | −50.4 | −210.9 |
C8H18 | 3-Methylheptane | −60.3 | −252.5 |
C8H18 | 4-Methylheptane | ? | ? |
C8H18 | 3-Ethylhexane | ? | ? |
C9Alkane branched isomers (selected) | |||
C9H20 | 2,2,4,4-Tetramethylpentane | −57.8 | −241.8 |
C9H20 | 2,2,3,3-Tetramethylpentane | −56.7 | −237.2 |
C9H20 | 2,2,3,4-Tetramethylpentane | −56.6 | −236.8 |
C9H20 | 2,3,3,4-Tetramethylpentane | −56.4 | −236.0 |
C9H20 | 3,3-Diethylpentane | −55.7 | −233.0 |
Other organic compounds
[edit]Species | Phase | Chemical formula | ΔfH⦵/(kJ/mol) |
---|---|---|---|
Acetone | Liquid | C3H6O | −248.4 |
Benzene | Liquid | C6H6 | 48.95 |
Benzoic acid | Solid | C7H6O2 | −385.2 |
Carbon tetrachloride | Liquid | CCl4 | −135.4 |
Carbon tetrachloride | Gas | CCl4 | −95.98 |
Ethanol | Liquid | C2H5OH | −277.0 |
Ethanol | Gas | C2H5OH | −235.3 |
Glucose | Solid | C6H12O6 | −1271 |
Isopropanol | Gas | C3H7OH | −318.1 |
Methanol(methyl alcohol) | Liquid | CH3OH | −238.4 |
Methanol(methyl alcohol) | Gas | CH3OH | −201.0 |
Methyl linoleate(Biodiesel) | Gas | C19H34O2 | −356.3 |
Sucrose | Solid | C12H22O11 | −2226.1 |
Trichloromethane(Chloroform) | Liquid | CHCl3 | −134.47 |
Trichloromethane(Chloroform) | Gas | CHCl3 | −103.18 |
Vinyl chloride | Solid | C2H3Cl | −94.12 |
See also
[edit]References
[edit]- ^IUPAC,Compendium of Chemical Terminology,2nd ed. (the "Gold Book" ) (1997). Online corrected version: (2006–) "standard pressure".doi:10.1351/goldbook.S05921
- ^Oxtoby, David W; Pat Gillis, H; Campion, Alan (2011).Principles of Modern Chemistry.Cengage Learning. p. 547.ISBN978-0-8400-4931-5.
- ^Moore, Stanitski, and Jurs.Chemistry: The Molecular Science.3rd edition. 2008.ISBN0-495-10521-X.pages 320–321.
- ^"Enthalpies of Reaction".science.uwaterloo.ca.Archivedfrom the original on 25 October 2017.Retrieved2 May2018.
- ^abHousecroft, C. E.; Sharpe, A. G. (2004).Inorganic Chemistry(2nd ed.). Prentice Hall. p. 392.ISBN978-0-13-039913-7.
- ^Green, D.W., ed. (2007).Perry's Chemical Engineers' Handbook(8th ed.). Mcgraw-Hill. pp. 2–191.ISBN9780071422949.
- ^Kleykamp, H. (1998). "Gibbs Energy of Formation of SiC: A contribution to the Thermodynamic Stability of the Modifications".Berichte der Bunsengesellschaft für physikalische Chemie.102(9): 1231–1234.doi:10.1002/bbpc.19981020928.
- ^"Silicon Carbide, Alpha (SiC)".March 1967.Retrieved5 February2019.
- Zumdahl, Steven (2009).Chemical Principles(6th ed.). Boston. New York: Houghton Mifflin. pp. 384–387.ISBN978-0-547-19626-8.