Standard enthalpy of formation

The standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements, with all substances in their standard states. The standard pressure value p^⦵ = 10⁵ Pa (= 100 kPa = 1 bar) is recommended by IUPAC, although prior to 1982 the value 1.00 atm (101.325 kPa) was used.^[1] There is no standard temperature. Its symbol is Δ_fH^⦵. The superscript Plimsoll on 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 as follows:

For a gas: the hypothetical state it would have assuming it obeyed the ideal gas equation at a pressure of 1 bar
For a solute present in an ideal solution: a concentration of exactly one mole per liter (1 M) at a pressure of 1 bar
For a pure substance or a solvent in a condensed state (a liquid or a solid): the standard state is the pure liquid or solid under a pressure of 1 bar
For an element: the form in which the element is most stable under 1 bar of pressure. One exception is phosphorus, for which the most stable form at 1 bar is black phosphorus, but white phosphorus is chosen as the standard reference state for zero enthalpy of formation.^[2]

For example, the standard enthalpy of formation of carbon dioxide would be the enthalpy of the following reaction under the above conditions:

C(s, graphite) + O₂(g) → CO₂(g)

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 in kilojoule per mole (kJ mol⁻¹), but also in kilocalorie per mole, joule per mole or kilocalorie per gram (any combination of these units conforming to the energy per mass or amount guideline).

In physics the energy per particle is often expressed in electronvolts (eV), where 1 eV corresponds to 96.485 kJ mol⁻¹.

All elements in their standard states (oxygen gas, solid carbon in the form of graphite, 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 atm, 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 symbol Δ_fH^⦵
_298 K.

Hess's law

For many substances, the formation reaction may be considered as the sum of a number of simpler reactions, either real or fictitious. The enthalpy of reaction can then be analyzed by applying Hess's Law, which states that the sum of the enthalpy changes for a number of individual reaction steps equals the enthalpy change of the overall reaction. This is true because enthalpy is a state 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

For ionic compounds, the standard enthalpy of formation is equivalent to the sum of several terms included in the Born–Haber cycle. For example, the formation of lithium fluoride,

Li(s) + 1⁄2 F₂(g) → LiF(s)

may be considered as the sum of several steps, each with its own enthalpy (or energy, approximately):

The standard enthalpy of atomization (or sublimation) of solid lithium.
The first ionization energy of gaseous lithium.
The standard enthalpy of atomization (or bond energy) of fluorine gas.
The electron affinity of a fluorine atom.
The lattice energy of lithium fluoride.

The sum of all these enthalpies will give the standard enthalpy of formation of lithium fluoride.

\Delta H_{\text{f}}=\Delta H_{\text{sub}}+{\text{IE}}_{\text{Li}}+{\frac {1}{2}}{\text{B(F–F)}}-{\text{EA}}_{\text{F}}-{\text{U}}_{\text{L}}.

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 in order to evaluate the lattice energy.^[3]

U_{\text{L}}=\Delta H_{\text{sub}}+{\text{IE}}_{\text{Li}}+{\frac {1}{2}}{\text{B(F–F)}}-{\text{EA}}_{\text{F}}+\Delta H_{\text{f}}.

Organic compounds

The formation reactions for most organic compounds are hypothetical. For instance, carbon and hydrogen will not directly react to form methane (CH₄), so that the standard enthalpy of formation cannot be measured directly. However the standard enthalpy of combustion is readily mesurable using bomb calorimetry. The standard enthalpy of formation is then determined using Hess's law. The combustion of methane (CH₄ + 2 O₂ → CO₂ + 2 H₂O) is equivalent to the sum of the hypothetical decomposition into elements followed by the combustion of the elements to form carbon dioxide and water:

CH₄ → C + 2 H₂

C + O₂ → CO₂

2 H₂ + O₂ → 2 H₂O

Applying Hess's law,

Δ_combH^⦵(CH₄) = [Δ_fH^⦵(CO₂) + 2 Δ_fH^⦵(H₂O)] − Δ_fH^⦵(CH₄).

Solving for the standard of enthalpy of formation,

Δ_fH^⦵(CH₄) = [Δ_fH^⦵(CO₂) + 2 Δ_fH^⦵(H₂O)] − Δ_combH^⦵(CH₄).

The value of Δ_fH^⦵(CH₄) is determined to be −74.8 kJ/mol. The negative sign shows that the reaction, if it were to proceed, would be exothermic; that is, methane is enthalpically more stable than hydrogen gas and carbon.

It is possible to predict heats of formation for simple unstrained organic compounds with the heat of formation group additivity method.

Use in calculation for other reactions

The standard enthalpy change of any reaction can 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 then minus the sum of the standard enthalpies of formation of the reactants (each being multiplied by its respective stoichiometric coefficient, ν) plus the 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]

Δ_rH^⦵ = Σν Δ_fH^⦵(products) − Σν Δ_fH^⦵(reactants).

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 of ideal solution between reactants and products where the enthalpy of mixing is zero.

For example, for the combustion of methane, CH₄ + 2 O₂ → CO₂ + 2 H₂O:

Δ_rH^⦵ = [Δ_fH^⦵(CO₂) + 2 Δ_fH^⦵(H₂O)] − [Δ_fH^⦵(CH₄) + 2 Δ_fH^⦵(O₂)].

However O₂ is an element in its standard state, so that Δ_fH^⦵(O₂) = 0, and the heat of reaction is simplified to

Δ_rH^⦵ = [Δ_fH^⦵(CO₂) + 2 Δ_fH^⦵(H₂O)] − Δ_fH^⦵(CH₄),

which is the equation in the previous section for the enthalpy of combustion Δ_combH^⦵.

Key concepts for doing enthalpy calculations

When a reaction is reversed, the magnitude of ΔH stays the same, but the sign changes.
When the balanced equation for a reaction is multiplied by an integer, the corresponding value of ΔH must 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. Allotropes of an element other than the standard state generally have non-zero standard enthalpies of formation.

Examples: standard enthalpies of formation at 25 °C

Thermochemical properties of selected substances at 298 K and 1 atm

Inorganic substances

Species	Phase	Chemical formula	Δ_fH^⦵ /(kJ/mol)
Aluminium
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
Ammonia (ammonium hydroxide)	Aqueous	NH₃ (NH₄OH)	−80.8
Ammonia	Gas	NH₃	−46.1
Ammonium nitrate	Solid	NH₄NO₃	−365.6
Barium
Barium chloride	Solid	BaCl₂	−858.6
Barium carbonate	Solid	BaCO₃	−1213
Barium hydroxide	Solid	Ba(OH)₂	−944.7
Barium oxide	Solid	BaO	−548.1
Barium sulfate	Solid	BaSO₄	−1473.2
Beryllium
Beryllium	Solid	Be	0
Beryllium hydroxide	Solid	Be(OH)₂	−902.9999
Beryllium oxide	Solid	BeO	−609.4(25)
Boron
Boron trichloride	Solid	BCl₃	−402.96
Bromine
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
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
Calcium
Calcium	Solid	Ca	0
Calcium	Gas	Ca	178.2
Calcium(II) ion	Gas	Ca²⁺	1925.90
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
Caesium
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
Carbon
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
Bicarbonate ion	Aqueous	HCO₃^–	−689.93
Carbonate ion	Aqueous	CO₃^2–	−675.23
Chlorine
Monatomic chlorine	Gas	Cl	121.7
Chloride ion	Aqueous	Cl⁻	−167.2
Chlorine	Gas	Cl₂	0
Chromium
Chromium	Solid	Cr	0
Copper
Copper	Solid	Cu	0
Copper(II) oxide	Solid	CuO	−155.2
Copper(II) sulfate	Aqueous	CuSO₄	−769.98
Fluorine
Fluorine	Gas	F₂	0
Hydrogen
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
Iodine	Solid	I₂	0
Iodine	Gas	I₂	62.438
Iodine	Aqueous	I₂	23
Iodide ion	Aqueous	I⁻	−55
Iron
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
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
Magnesium
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
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
Mercury(II) oxide (red)	Solid	HgO	−90.83
Mercury sulfide (red, cinnabar)	Solid	HgS	−58.2
Nitrogen
Ammonia	Aqueous	NH₃	−80.8
Ammonia	Gas	NH₃	−45.90
Ammonium chloride	Solid	NH₄Cl	−314.55
Nitrogen dioxide	Gas	NO₂	33.2
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
Oxygen
Monatomic oxygen	Gas	O	249
Oxygen	Gas	O₂	0
Ozone	Gas	O₃	143
Phosphorus
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
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 perchlorate	Solid	KClO₄	−430.12
Silicon
Silicon	Gas	Si	368.2
Silicon carbide	Solid	SiC	−73.22
Silicon tetrachloride	Liquid	SiCl₄	−640.1
Silica (Quartz)	Solid	SiO₂	−910.86
Silver
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
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
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
Tin
Titanium
Titanium	Gas	Ti	468
Titanium tetrachloride	Gas	TiCl₄	−763.2
Titanium tetrachloride	Liquid	TiCl₄	−804.2
Titanium dioxide	Solid	TiO₂	−944.7
Zinc
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

Formula	Name	Δ_fH^⦵ /(kcal/mol)	Δ_fH^⦵ /(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
C₄ Alkane branched isomers
C₄H₁₀	Isobutane (methylpropane)	−32.1	−134.3
C₅ Alkane branched isomers
C₅H₁₂	Neopentane (dimethylpropane)	−40.1	−167.8
C₅H₁₂	Isopentane (methylbutane)	−36.9	−154.4
C₆ Alkane 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
C₇ Alkane 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
C₈ Alkane 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	?	?
C₉ Alkane 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

Species	Phase	Chemical formula	Δ_fH^⦵ /(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

References

^ 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. p. 547. ISBN 0-8400-4931-5.
^ Moore, Stanitski, and Jurs. Chemistry: The Molecular Science. 3rd edition. 2008. ISBN 0-495-10521-X. pages 320–321.
^ "Enthalpies of Reaction". www.science.uwaterloo.ca. Archived from the original on 25 October 2017. Retrieved 2 May 2018. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
^ ^a ^b Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 392. ISBN 978-0-13-039913-7.
^ Green, D.W., ed. (2007). Perry's Chemical Engineers' Handbook (8th ed.). Mcgraw-Hill. p. 2-191. ISBN 9780071422949.

Zumdahl, Steven (2009). Chemical Principles (6th ed.). Boston. New York: Houghton Mifflin. pp. 384–387. ISBN 978-0-547-19626-8.

External links

NIST Chemistry WebBook

[1] IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "standard pressure". doi:10.1351/goldbook.S05921

[2] Oxtoby, David W; Pat Gillis, H; Campion, Alan (2011). Principles of Modern Chemistry. p. 547. ISBN 0-8400-4931-5.

[3] Moore, Stanitski, and Jurs. Chemistry: The Molecular Science. 3rd edition. 2008. ISBN 0-495-10521-X. pages 320–321.

[4] "Enthalpies of Reaction". www.science.uwaterloo.ca. Archived from the original on 25 October 2017. Retrieved 2 May 2018. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)

[HS-5] Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 392. ISBN 978-0-13-039913-7.

[6] Green, D.W., ed. (2007). Perry's Chemical Engineers' Handbook (8th ed.). Mcgraw-Hill. p. 2-191. ISBN 9780071422949.

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