Hydrogen

Formula: H₂
Molecular weight: 2.01588
IUPAC Standard InChI: InChI=1S/H2/h1H
IUPAC Standard InChIKey: UFHFLCQGNIYNRP-UHFFFAOYSA-N
CAS Registry Number: 1333-74-0
Chemical structure:
This structure is also available as a 2d Mol file or as a computed 3d SD file
The 3d structure may be viewed using Java or Javascript.
Isotopologues:
Other names: Dihydrogen; o-Hydrogen; p-Hydrogen; Molecular hydrogen; H2; UN 1049; UN 1966
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- Electron-Impact Ionization Cross Sections (on physics web site)
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Gas phase thermochemistry data

Go To: Top, Reaction thermochemistry data, Gas phase ion energetics data, References, Notes

Quantity	Value	Units	Method	Reference	Comment
S°_{gas,1 bar}	130.680 ± 0.003	J/mol*K	Review	Cox, Wagman, et al., 1984	CODATA Review value
S°_{gas,1 bar}	130.68	J/mol*K	Review	Chase, 1998	Data last reviewed in March, 1977

Gas Phase Heat Capacity (Shomate Equation)

C_p° = A + B*t + C*t² + D*t³ + E/t²
H° − H°_298.15= A*t + B*t²/2 + C*t³/3 + D*t⁴/4 − E/t + F − H
S° = A*ln(t) + B*t + C*t²/2 + D*t³/3 − E/(2*t²) + G
C_p = heat capacity (J/mol*K)
H° = standard enthalpy (kJ/mol)
S° = standard entropy (J/mol*K)
t = temperature (K) / 1000.

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View table.

Temperature (K)	298. to 1000.	1000. to 2500.	2500. to 6000.
A	33.066178	18.563083	43.413560
B	-11.363417	12.257357	-4.293079
C	11.432816	-2.859786	1.272428
D	-2.772874	0.268238	-0.096876
E	-0.158558	1.977990	-20.533862
F	-9.980797	-1.147438	-38.515158
G	172.707974	156.288133	162.081354
H	0.0	0.0	0.0
Reference	Chase, 1998	Chase, 1998	Chase, 1998
Comment	Data last reviewed in March, 1977; New parameter fit October 2001	Data last reviewed in March, 1977; New parameter fit October 2001	Data last reviewed in March, 1977; New parameter fit October 2001

Reaction thermochemistry data

Go To: Top, Gas phase thermochemistry data, Gas phase ion energetics data, References, Notes

Data compiled as indicated in comments:
MS - José A. Martinho Simões
M - Michael M. Meot-Ner (Mautner) and Sharon G. Lias
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein
B - John E. Bartmess

Note: Please consider using the reaction search for this species. This page allows searching of all reactions involving this species. A general reaction search form is also available. Future versions of this site may rely on reaction search pages in place of the enumerated reaction displays seen below.

Reactions 1 to 50

(solution) + Hydrogen (solution) = 2 (solution)

By formula: C₈Co₂O₈ (solution) + H₂ (solution) = 2C₄HCoO₄ (solution)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	19.7 ± 0.8	kJ/mol	EqS	Rathke, Klingler, et al., 1992	solvent: Supercritical carbon dioxide; Temperature range: 333-453 K. The results corrected for 1 atm pressure of H2 are 16.7 kJ/mol and -17.6 J/(mol K) Rathke, Klingler, et al., 1992; MS
Δ_rH°	13.0 ± 0.9	kJ/mol	EqS	Bor, 1986	solvent: n-Hexane; Temperature range: ca. 300-420 K; MS
Δ_rH°	26.4	kJ/mol	KinS	Alemdaroglu, Penninger, et al., 1976	solvent: n-Heptane; The reaction enthalpy relies on the experimental values for the forward and reverse activation enthalpies, 72.4 and 46.0 kJ/mol, respectively Alemdaroglu, Penninger, et al., 1976. A rather different value has, however, been reported for the activation enthalpy of the forward reaction, 104.6 kJ/mol Ungváry, 1972; MS
Δ_rH°	27.6	kJ/mol	EqS	Alemdaroglu, Penninger, et al., 1976	solvent: n-Heptane; Temperature range: 353-428 K; MS
Δ_rH°	13.4	kJ/mol	EqS	Ungváry, 1972	solvent: n-Heptane; Temperature range: 307-428 K. The results corrected for 1 atm pressure of H2 are 18.0 kJ/mol and -10.9 J/(mol K) Rathke, Klingler, et al., 1992; MS

H₃⁺ + Hydrogen = (H₃⁺ • )

By formula: H₃⁺ + H₂ = (H₃⁺ • H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	29. ± 2.	kJ/mol	AVG	N/A	Average of 4 out of 11 values; Individual data points
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	72.8 to 72.8	J/mol*K	RNG	N/A	Range of 6 values; Individual data points

C₁₁H₂O₁₁Os (solution) + (solution) = Hydrogen (g) + (solution)

By formula: C₁₁H₂O₁₁Os (solution) + CO (solution) = H₂ (g) + C₁₂O₁₂Os₃ (solution)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-37.7 ± 9.6	kJ/mol	ES/KS	Poë, Sampson, et al., 1993	solvent: Decalin; Calculated from equilibrium and kinetic data Poë, Sampson, et al., 1993.; MS
Δ_rH°	-77.4 ± 9.7	kJ/mol	N/A	Poë, Sampson, et al., 1993	solvent: Decalin; Calculated from data for the reactions Os3(CO)10(H)2(solution) + CO(solution) = Os3(CO)11(H)2(solution) (hrxn [kJ/mol]=-39.7±1.3, srxn [J/(mol K)]=-80.3±3.8) and Os3(CO)11(H)2(solution) + CO(solution) = Os3(CO)12(solution) + H2(g) (hrxn [kJ/mol]=-37.7±9.6, srxn [J/(mol K)]=-32.6±27.6) Poë, Sampson, et al., 1993.; MS

+ Hydrogen =

By formula: C₆H₁₀ + H₂ = C₆H₁₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-118. ± 6.	kJ/mol	AVG	N/A	Average of 8 values; Individual data points

(cr) + Hydrogen (g) = 2C₈H₆CrO₃ (cr)

By formula: C₁₆H₁₀Cr₂O₆ (cr) + H₂ (g) = 2C₈H₆CrO₃ (cr)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-13.9 ± 4.0	kJ/mol	RSC	Landrum and Hoff, 1985	The reaction enthalpy was obtained from the value for the reaction 2Cr(Cp)(CO)3(H)(cr) + 1,3-cy-C6H8(solution) = [Cr(Cp)(CO)3]2(cr) + cy-C6H10(solution), -98.3 ± 3.8 kJ/mol Landrum and Hoff, 1985, together with the calculated enthalpy for 1,3-cy-C6H8(l) + H2(g) = cy-C6H10(l), -112.2±1.3 Pedley, 1994. It was assumed that 1,3-cy-C6H8 and cy-C6H10 have similar solution enthalpies in heptane; MS
Δ_rH°	-15.1 ± 4.2	kJ/mol	DSC	Landrum and Hoff, 1985	The reaction enthalpy was obtained from the value for the reaction 2Cr(Cp)(CO)3(H)(cr) + 1,3-cy-C6H8(solution) = [Cr(Cp)(CO)3]2(cr) + cy-C6H10(solution), -98.3 ± 3.8 kJ/mol Landrum and Hoff, 1985, together with the calculated enthalpy for 1,3-cy-C6H8(l) + H2(g) = cy-C6H10(l), -112.2±1.3 Pedley, 1994. It was assumed that 1,3-cy-C6H8 and cy-C6H10 have similar solution enthalpies in heptane; MS

Hydrogen + =

By formula: H₂ + C₆H₁₂ = C₆H₁₄

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-125. ± 3.	kJ/mol	AVG	N/A	Average of 8 values; Individual data points

(H₃⁺ • Hydrogen ) + = (H₃⁺ • 2)

By formula: (H₃⁺ • H₂) + H₂ = (H₃⁺ • 2H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	14. ± 0.8	kJ/mol	PHPMS	Hiraoka, 1987	gas phase; M
Δ_rH°	13.	kJ/mol	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase; M
Δ_rH°	14.	kJ/mol	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase; deuterated; M
Δ_rH°	17.	kJ/mol	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M
Δ_rH°	7.5	kJ/mol	HPMS	Bennett and Field, 1972	gas phase; Entropy change is questionable; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	72.8	J/mol*K	PHPMS	Hiraoka, 1987	gas phase; M
Δ_rS°	70.7	J/mol*K	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase; M
Δ_rS°	67.4	J/mol*K	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase; deuterated; M
Δ_rS°	82.8	J/mol*K	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M
Δ_rS°	45.2	J/mol*K	HPMS	Bennett and Field, 1972	gas phase; Entropy change is questionable; M

Hydrogen + =

By formula: H₂ + C₇H₁₄ = C₇H₁₆

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-125. ± 2.	kJ/mol	AVG	N/A	Average of 6 values; Individual data points

+ Hydrogen =

By formula: C₈H₁₆ + H₂ = C₈H₁₈

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-125. ± 6.	kJ/mol	AVG	N/A	Average of 7 values; Individual data points

+ = Hydrogen

By formula: H^- + H⁺ = H₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	1675.3	kJ/mol	N/A	Shiell, Hu, et al., 2000	gas phase; Given: 139714.8±1 cm-1 at 0K, or 399.465±0.003 kcal/mol; B
Δ_rH°	1675.3	kJ/mol	N/A	Pratt, McCormack, et al., 1992	gas phase; 399.46±0.01 kcal/mol at 0K; 0.94 correction, Gurvich, Veyts, et al.; B
Δ_rH°	1675.3	kJ/mol	D-EA	Lykke, Murray, et al., 1991	gas phase; Reported: 6082.99±0.15 cm-1, or 0.754195(18) eV; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	1649.3 ± 0.42	kJ/mol	H-TS	Shiell, Hu, et al., 2000	gas phase; Given: 139714.8±1 cm-1 at 0K, or 399.465±0.003 kcal/mol; B
Δ_rG°	1649.3	kJ/mol	H-TS	Lykke, Murray, et al., 1991	gas phase; Reported: 6082.99±0.15 cm-1, or 0.754195(18) eV; B

Hydrogen + =

By formula: H₂ + C₅H₈ = C₅H₁₀

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-112.7 ± 0.54	kJ/mol	Chyd	Allinger, Dodziuk, et al., 1982	liquid phase; solvent: Hexane; ALS
Δ_rH°	-112. ± 0.8	kJ/mol	Chyd	Roth and Lennartz, 1980	liquid phase; solvent: Cyclohexane; ALS
Δ_rH°	-109.0 ± 1.8	kJ/mol	Chyd	Turner, Jarrett, et al., 1973	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-110. ± 0.8	kJ/mol	Chyd	Rogers and McLafferty, 1971	liquid phase; solvent: Hydrocarbon; ALS
Δ_rH°	-111.6 ± 0.3	kJ/mol	Chyd	Dolliver, Gresham, et al., 1937	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -112.6 ± 0.3 kJ/mol; At 355 °K; ALS

Hydrogen + =

By formula: H₂ + C₈H₁₄ = C₈H₁₆

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-102.	kJ/mol	Chyd	Doering, Roth, et al., 1989	liquid phase; ALS
Δ_rH°	-103. ± 0.8	kJ/mol	Chyd	Roth and Lennartz, 1980	liquid phase; solvent: Cyclohexane; ALS
Δ_rH°	-96.40 ± 0.71	kJ/mol	Chyd	Rogers, Von Voithenberg, et al., 1978	liquid phase; solvent: Hexane; ALS
Δ_rH°	-96.1 ± 0.4	kJ/mol	Chyd	Turner and Meador, 1957	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-97.40 ± 0.63	kJ/mol	Chyd	Conn, Kistiakowsky, et al., 1939	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -98.4 ± 0.2 kJ/mol; At 355 K; ALS

0.5C₃₆H₈₄Cl₂P₄Rh₂ (solution) + Hydrogen (g) = C₁₈H₄₄ClP₂Rh (solution)

By formula: 0.5C₃₆H₈₄Cl₂P₄Rh₂ (solution) + H₂ (g) = C₁₈H₄₄ClP₂Rh (solution)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-98.8 ± 2.7	kJ/mol	RSC	Wang, Rosini, et al., 1995	solvent: Benzene; The reaction enthalpy was calculated from the enthalpies of the reactions Rh[P(i-Pr)3]2(Cl)(H)2(solution) + t-BuNC(solution) = Rh[P(i-Pr)3]2(Cl)(CN-t-Bu)(solution) + H2(g), -41.4 ± 1.7 kJ/mol, and 0.5{Rh[P(i-Pr)3]2(Cl)}2(solution) + t-BuNC(solution) = Rh[P(i-Pr)3]2(Cl)(CN-t-Bu)(solution), -140.2 ± 2.1 kJ/mol Wang, Rosini, et al., 1995. The enthalpy of solution of {Rh[P(i-Pr)3]2(Cl)}2(cr) was measured as 20.1 ± 1.3 kJ/mol Wang, Rosini, et al., 1995.; MS

Hydrogen + =

By formula: H₂ + C₆H₁₀ = C₆H₁₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-100.8 ± 0.63	kJ/mol	Chyd	Rogers, Crooks, et al., 1987	liquid phase; ALS
Δ_rH°	-101.3 ± 0.50	kJ/mol	Chyd	Allinger, Dodziuk, et al., 1982	liquid phase; solvent: Hexane; ALS
Δ_rH°	-96.3 ± 0.2	kJ/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-96.3 ± 0.2	kJ/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-96.3 ± 0.2	kJ/mol	Chyd	Turner and Garner, 1957, 2	liquid phase; solvent: Acetic acid; ALS

2 Hydrogen + =

By formula: 2H₂ + C₆H₁₀ = C₆H₁₄

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-252. ± 2.	kJ/mol	Chyd	Fang and Rogers, 1992	liquid phase; solvent: Cyclohexane; ALS
Δ_rH°	-253.9 ± 2.7	kJ/mol	Chyd	Molnar, Rachford, et al., 1984	liquid phase; solvent: Dioxane; ALS
Δ_rH°	-251.8 ± 1.5	kJ/mol	Chyd	Turner, Mallon, et al., 1973	liquid phase; solvent: Glacial acetic acid; ALS
Δ_rH°	-251.2 ± 0.42	kJ/mol	Chyd	Kistiakowsky, Ruhoff, et al., 1936	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -253.3 ± 0.63 kJ/mol; At 355 °K; ALS

Hydrogen + =

By formula: H₂ + C₇H₁₂ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-101.9 ± 0.63	kJ/mol	Chyd	Allinger, Dodziuk, et al., 1982	liquid phase; solvent: Hexane; ALS
Δ_rH°	-98.3 ± 0.8	kJ/mol	Chyd	Rogers and McLafferty, 1971	liquid phase; solvent: Hydrocarbon; ALS
Δ_rH°	-98.58 ± 0.46	kJ/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-98.58 ± 0.46	kJ/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS

Hydrogen + =

By formula: H₂ + C₇H₁₂ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-106.9 ± 0.4	kJ/mol	Chyd	Allinger, Dodziuk, et al., 1982	liquid phase; solvent: Hexane; ALS
Δ_rH°	-101. ± 0.8	kJ/mol	Chyd	Rogers and McLafferty, 1971	liquid phase; solvent: Hydrocarbon; ALS
Δ_rH°	-104.1 ± 0.50	kJ/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-104.1 ± 0.50	kJ/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS

Hydrogen + =

By formula: H₂ + C₆H₁₀ = C₆H₁₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-115.9 ± 0.96	kJ/mol	Chyd	Allinger, Dodziuk, et al., 1982	liquid phase; solvent: Hexane; ALS
Δ_rH°	-112.5 ± 0.08	kJ/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-112.3 ± 0.2	kJ/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-112.2 ± 0.3	kJ/mol	Chyd	Turner and Garner, 1957, 2	liquid phase; solvent: Acetic acid; ALS

C₃H₇⁺ + Hydrogen = (C₃H₇⁺ • )

By formula: C₃H₇⁺ + H₂ = (C₃H₇⁺ • H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	10.	kJ/mol	PHPMS	Hiraoka and Kebarle, 1976	gas phase; Entropy change calculated or estimated, DG<, Δ_rH<; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	84.	J/mol*K	N/A	Hiraoka and Kebarle, 1976	gas phase; Entropy change calculated or estimated, DG<, Δ_rH<; M

Free energy of reaction

Δ_rG° (kJ/mol)	T (K)	Method	Reference	Comment
4.	170.	PHPMS	Hiraoka and Kebarle, 1976	gas phase; Entropy change calculated or estimated, DG<, Δ_rH<; M

+ Hydrogen = ( • )

By formula: Co⁺ + H₂ = (Co⁺ • H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	82. ± 4.	kJ/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(O K)=76.1 kJ/mol, Δ_rS(300 K)=86.2 J/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	92.0	J/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(O K)=76.1 kJ/mol, Δ_rS(300 K)=86.2 J/mol*K; M

Enthalpy of reaction

Δ_rH° (kJ/mol)	T (K)	Method	Reference	Comment
73.2 (+9.6,-0.)		CID	Haynes and Armentrout, 1996	gas phase; guided ion beam CID; M

+ Hydrogen =

By formula: C₅H₁₀ + H₂ = C₅H₁₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-126.6 ± 2.4	kJ/mol	Chyd	Molnar, Rachford, et al., 1984	liquid phase; solvent: Dioxane; ALS
Δ_rH°	-125.0 ± 1.8	kJ/mol	Chyd	Molnar, Rachford, et al., 1984	liquid phase; solvent: Hexane; ALS
Δ_rH°	-122.6 ± 2.4	kJ/mol	Chyd	Rogers and Skanupong, 1974	liquid phase; solvent: Hexane; ALS
Δ_rH°	-119. ± 1.	kJ/mol	Chyd	Rogers and McLafferty, 1971	liquid phase; solvent: Hydrocarbon; ALS

+ Hydrogen =

By formula: C₇H₁₂ + H₂ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-119.5 ± 0.65	kJ/mol	Chyd	Rogers, Crooks, et al., 1987	liquid phase; ALS
Δ_rH°	-116.1 ± 0.54	kJ/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-116.1 ± 0.54	kJ/mol	Eqk	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-120.1 ± 0.3	kJ/mol	Chyd	Turner and Garner, 1957, 2	liquid phase; solvent: Acetic acid; ALS

Hydrogen + =

By formula: H₂ + C₇H₁₂ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-110. ± 0.4	kJ/mol	Chyd	Roth and Lennartz, 1980	liquid phase; solvent: Cyclohexane; ALS
Δ_rH°	-108.2 ± 0.4	kJ/mol	Chyd	Turner, Meador, et al., 1957	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-108.9 ± 0.63	kJ/mol	Chyd	Conn, Kistiakowsky, et al., 1939	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -111.0 ± 0.08 kJ/mol; At 355 K; ALS

3 Hydrogen + =

By formula: 3H₂ + C₇H₈ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-305. ± 0.4	kJ/mol	Chyd	Roth, Klaerner, et al., 1983	liquid phase; solvent: Isooctane; ALS
Δ_rH°	-294.9 ± 1.6	kJ/mol	Chyd	Turner, Meador, et al., 1957	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-301.7 ± 1.3	kJ/mol	Chyd	Conn, Kistiakowsky, et al., 1939	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -304.8 ± 0.04 kJ/mol; at 355 K; ALS

2 Hydrogen + =

By formula: 2H₂ + C₆H₁₀ = C₆H₁₄

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-231.4 ± 3.0	kJ/mol	Chyd	Molnar, Rachford, et al., 1984	liquid phase; solvent: Dioxane; ALS
Δ_rH°	-227.0 ± 2.8	kJ/mol	Chyd	Molnar, Rachford, et al., 1984	liquid phase; solvent: Hexane; ALS
Δ_rH°	-223.4 ± 0.63	kJ/mol	Chyd	Dolliver, Gresham, et al., 1937	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -225.4 ± 0.63 kJ/mol; At 355 °K; ALS

+ 3 Hydrogen =

By formula: C₅H₅N + 3H₂ = C₅H₁₁N

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-193.8 ± 0.75	kJ/mol	Eqk	Hales and Herington, 1957	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -202.2 ± 0.75 kJ/mol; At 400-550 K; ALS
Δ_rH°	-193.0 ± 2.1	kJ/mol	Eqk	Burrows and King, 1935	liquid phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -188.3 kJ/mol; At 423-443 K; ALS

+ Hydrogen =

By formula: C₈H₁₆ + H₂ = C₈H₁₈

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-107.	kJ/mol	Chyd	Turner, Nettleton, et al., 1958	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-112.9 ± 0.3	kJ/mol	Chyd	Dolliver, Gresham, et al., 1937	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -114.0 ± 0.3 kJ/mol; At 355 °K; ALS
Δ_rH°	-119.6 ± 3.3	kJ/mol	Chyd	Crawford and Parks, 1936	liquid phase; ALS

+ Hydrogen =

By formula: C₃H₆ + H₂ = C₃H₈

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-123.4 ± 5.0	kJ/mol	Chyd	Kistiakowsky and Nickle, 1951	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -124.9 ± 2.1 kJ/mol; ALS
Δ_rH°	-125.0 ± 0.42	kJ/mol	Chyd	Kistiakowsky, Ruhoff, et al., 1935	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -126.00 ± 0.054 kJ/mol; At 355 °K; ALS

( • ) + Hydrogen = ( • • )

By formula: (Co⁺ • CH₄) + H₂ = (Co⁺ • H₂ • CH₄)

Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	95.8	J/mol*K	SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; switching reaction(Co+).2H2, Δ_rS(440 K); Kemper, Bushnell, et al., 1993; M

Enthalpy of reaction

Δ_rH° (kJ/mol)	T (K)	Method	Reference	Comment
73. (+3.,-0.)		SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; switching reaction(Co+).2H2, Δ_rS(440 K); Kemper, Bushnell, et al., 1993; M

Hydrogen + =

By formula: H₂ + C₃H₆O = C₃H₈O

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-68.74 ± 0.42	kJ/mol	Cm	Wiberg, Crocker, et al., 1991	liquid phase; ALS
Δ_rH°	-55.23	kJ/mol	Eqk	Buckley and Herington, 1965	gas phase; ALS
Δ_rH°	-55.40 ± 0.42	kJ/mol	Chyd	Dolliver, Gresham, et al., 1938	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -56.1 ± 0.4 kJ/mol; At 355 °K; ALS

( • Hydrogen ) + = ( • • )

By formula: (Co⁺ • H₂) + CH₄ = (Co⁺ • CH₄ • H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	91.2	J/mol*K	SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; switching reaction(Co+)2H2, Δ_rS(440 K); Kemper, Bushnell, et al., 1993; M

Enthalpy of reaction

Δ_rH° (kJ/mol)	T (K)	Method	Reference	Comment
94.6 (+5.0,-0.)		SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; switching reaction(Co+)2H2, Δ_rS(440 K); Kemper, Bushnell, et al., 1993; M

+ Hydrogen =

By formula: C₈H₁₄ + H₂ = C₈H₁₆

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-110. ± 1.	kJ/mol	Chyd	Rogers and McLafferty, 1971	liquid phase; solvent: Hydrocarbon; ALS
Δ_rH°	-110.1 ± 0.2	kJ/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-110.1 ± 0.2	kJ/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS

Hydrogen + =

By formula: H₂ + C₈H₁₄ = C₈H₁₆

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-144. ± 0.4	kJ/mol	Chyd	Roth, Adamczak, et al., 1991	liquid phase; see Doering, Roth, et al., 1989; ALS
Δ_rH°	-144.0 ± 1.8	kJ/mol	Chyd	Rogers, Von Voithenberg, et al., 1978	liquid phase; solvent: Hexane; ALS
Δ_rH°	-134.9 ± 0.88	kJ/mol	Chyd	Turner and Meador, 1957	liquid phase; solvent: Acetic acid; ALS

( • Hydrogen ) + = ( • 2)

By formula: (Co⁺ • H₂) + H₂ = (Co⁺ • 2H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	75. ± 3.	kJ/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=71.1 kJ/mol, Δ_rS(300 K)=103. J/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	103.	J/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=71.1 kJ/mol, Δ_rS(300 K)=103. J/mol*K; M

( • 2 Hydrogen ) + = ( • 3)

By formula: (Co⁺ • 2H₂) + H₂ = (Co⁺ • 3H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	44. ± 2.	kJ/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=40. kJ/mol, Δ_rS(300 K)=85.8 J/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	85.8	J/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=40. kJ/mol, Δ_rS(300 K)=85.8 J/mol*K; M

( • 3 Hydrogen ) + = ( • 4)

By formula: (Co⁺ • 3H₂) + H₂ = (Co⁺ • 4H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	44. ± 3.	kJ/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=40. kJ/mol, Δ_rS(300 K)=105. J/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	101.	J/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=40. kJ/mol, Δ_rS(300 K)=105. J/mol*K; M

( • 4 Hydrogen ) + = ( • 5)

By formula: (Co⁺ • 4H₂) + H₂ = (Co⁺ • 5H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	22. ± 3.	kJ/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=18. kJ/mol, Δ_rS(300 K)=91.6 J/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	94.1	J/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=18. kJ/mol, Δ_rS(300 K)=91.6 J/mol*K; M

( • 5 Hydrogen ) + = ( • 6)

By formula: (Co⁺ • 5H₂) + H₂ = (Co⁺ • 6H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	20. ± 3.	kJ/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=17. kJ/mol, Δ_rS(300 K)=99.6 J/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	99.2	J/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=17. kJ/mol, Δ_rS(300 K)=99.6 J/mol*K; M

( • 6 Hydrogen ) + = ( • 7)

By formula: (Co⁺ • 6H₂) + H₂ = (Co⁺ • 7H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	6. ± 3.	kJ/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=3. kJ/mol; Δ_rS(300 K)=75.3 J/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	75.3	J/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; Δ_rH(0 K)=3. kJ/mol; Δ_rS(300 K)=75.3 J/mol*K; M

(H₃⁺ • 3 Hydrogen ) + = (H₃⁺ • 4)

By formula: (H₃⁺ • 3H₂) + H₂ = (H₃⁺ • 4H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	7.2 ± 0.4	kJ/mol	PHPMS	Hiraoka, 1987	gas phase; M
Δ_rH°	10.	kJ/mol	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	74.9	J/mol*K	PHPMS	Hiraoka, 1987	gas phase; M
Δ_rS°	80.8	J/mol*K	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M

(H₃⁺ • 2 Hydrogen ) + = (H₃⁺ • 3)

By formula: (H₃⁺ • 2H₂) + H₂ = (H₃⁺ • 3H₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	13. ± 0.4	kJ/mol	PHPMS	Hiraoka, 1987	gas phase; M
Δ_rH°	16.	kJ/mol	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	77.4	J/mol*K	PHPMS	Hiraoka, 1987	gas phase; M
Δ_rS°	84.5	J/mol*K	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M

Hydrogen + =

By formula: H₂ + C₈H₁₆ = C₈H₁₈

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-118.2 ± 0.4	kJ/mol	Chyd	Rogers, Dejroongruang, et al., 1992	liquid phase; solvent: Cyclohexane; ALS
Δ_rH°	-119.7 ± 2.2	kJ/mol	Chyd	Rogers and Siddiqui, 1975	liquid phase; solvent: n-Hexane; ALS
Δ_rH°	-114.6 ± 0.59	kJ/mol	Chyd	Turner, Jarrett, et al., 1973	liquid phase; solvent: Acetic acid; ALS

2 Hydrogen + =

By formula: 2H₂ + C₈H₁₄ = C₈H₁₈

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-268.7 ± 1.1	kJ/mol	Chyd	Rogers, Dagdagan, et al., 1979	liquid phase; solvent: Hexane; ALS
Δ_rH°	-262.8 ± 0.67	kJ/mol	Chyd	Turner, Jarrett, et al., 1973	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-263.	kJ/mol	Chyd	Sicher, Svoboda, et al., 1966	liquid phase; solvent: Acetic acid; ALS

Hydrogen + =

By formula: H₂ + C₈H₁₄O = C₈H₁₆O

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-55.73	kJ/mol	Chyd	Wiberg, Crocker, et al., 1991	liquid phase; ALS
Δ_rH°	-53.14	kJ/mol	Chyd	Wiberg, Crocker, et al., 1991	solid phase; ALS
Δ_rH°	-39.0	kJ/mol	Chyd	Wiberg, Crocker, et al., 1991	gas phase; ALS
Δ_rH°	-53.14 ± 0.59	kJ/mol	Cm	Wiberg, Crocker, et al., 1991	solid phase; ALS

Hydrogen + =

By formula: H₂ + C₇H₁₂ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-111.4 ± 0.37	kJ/mol	Chyd	Rogers, Crooks, et al., 1987	liquid phase; ALS
Δ_rH°	-106.3 ± 0.46	kJ/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
Δ_rH°	-106.3 ± 0.46	kJ/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS

2 Hydrogen + =

By formula: 2H₂ + C₇H₁₀ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-208.9 ± 0.3	kJ/mol	Chyd	Turner, Mallon, et al., 1973	liquid phase; solvent: Glacial acetic acid; ALS
Δ_rH°	-212.4 ± 0.63	kJ/mol	Chyd	Conn, Kistiakowsky, et al., 1939	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -214.5 ± 0.2 kJ/mol; At 355 K; ALS

Hydrogen + =

By formula: H₂ + C₇H₁₀ = C₇H₁₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-137. ± 0.4	kJ/mol	Chyd	Doering, Roth, et al., 1988	gas phase; ALS
Δ_rH°	-141.5 ± 1.2	kJ/mol	Chyd	Rogers, Choi, et al., 1980	liquid phase; solvent: Hexane; Author was aware that data differs from previously reported values; ALS
Δ_rH°	-138.6 ± 0.88	kJ/mol	Chyd	Turner, Meador, et al., 1957	liquid phase; solvent: Acetic acid; ALS

+ Hydrogen =

By formula: C₃H₆O + H₂ = C₃H₈O

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-84.3 ± 0.4	kJ/mol	Cm	Wiberg, Crocker, et al., 1991	liquid phase; solvent: Triglyme; Heat of hydrogenation; ALS
Δ_rH°	-69.55 ± 0.76	kJ/mol	Eqk	Connett, 1972	gas phase; At 473-524 K; ALS
Δ_rH°	-65.77 ± 0.67	kJ/mol	Chyd	Buckley and Cox, 1967	gas phase; ALS

2 Hydrogen + =

By formula: 2H₂ + C₆H₈ = C₆H₁₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-224.4 ± 1.2	kJ/mol	Chyd	Turner, Mallon, et al., 1973	liquid phase; solvent: Glacial acetic acid; ALS
Δ_rH°	-229.6 ± 0.42	kJ/mol	Chyd	Kistiakowsky, Ruhoff, et al., 1936	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -231.7 ± 0.4 kJ/mol; At 355 °K; ALS

(solution) + Hydrogen (solution) = 2 (solution)

By formula: C₁₀Mn₂O₁₀ (solution) + H₂ (solution) = 2C₅HMnO₅ (solution)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	36.4 ± 1.3	kJ/mol	EqS	Klingler R.J. and Rathke, 1992	solvent: Supercritical carbon dioxide; Temperature range: 373-463 K; MS

Gas phase ion energetics data

Go To: Top, Gas phase thermochemistry data, Reaction thermochemistry data, References, Notes

Data evaluated as indicated in comments:
HL - Edward P. Hunter and Sharon G. Lias
L - Sharon G. Lias

Data compiled as indicated in comments:
B - John E. Bartmess
LL - Sharon G. Lias and Joel F. Liebman
LBLHLM - Sharon G. Lias, John E. Bartmess, Joel F. Liebman, John L. Holmes, Rhoda D. Levin, and W. Gary Mallard
LLK - Sharon G. Lias, Rhoda D. Levin, and Sherif A. Kafafi
RDSH - Henry M. Rosenstock, Keith Draxl, Bruce W. Steiner, and John T. Herron

View reactions leading to H₂⁺ (ion structure unspecified)

Quantity	Value	Units	Method	Reference	Comment
IE (evaluated)	15.42593 ± 0.00005	eV	N/A	N/A	L
Quantity	Value	Units	Method	Reference	Comment
Proton affinity (review)	422.3	kJ/mol	N/A	Hunter and Lias, 1998	HL
Quantity	Value	Units	Method	Reference	Comment
Gas basicity	394.7	kJ/mol	N/A	Hunter and Lias, 1998	HL

Ionization energy determinations

IE (eV)	Method	Reference	Comment
15.425927	EVAL	Shiner, Gilligan, et al., 1993	T = 0K; LL
15.425930	EVAL	Shiner, Gilligan, et al., 1993	T = 0K; LL
15.425932 ± 0.000002	S	McCormack, Gilligan, et al., 1989	T = 0K; LL
15.429558 ± 0.00001	LS	Glab and Hessler, 1987	T = 0K; LBLHLM
15.433174 ± 0.00001	LS	Glab and Hessler, 1987	T = 0K; LBLHLM
15.425942 ± 0.00001	LS	Glab and Hessler, 1987	T = 0K; LBLHLM
15.425932	S	Eyler, Short, et al., 1986	T = 0K; LBLHLM
15.425929	S	Eyler, Short, et al., 1986	T = 0K; LBLHLM
15.425930 ± 0.000027	N/A	Eyler, Short, et al., 1986	LBLHLM
15.5 ± 1.0	S	Farber, Srivastava, et al., 1982	LBLHLM
15.98	PE	Kimura, Katsumata, et al., 1981	LLK
15.43	PE	Bieri, Schmelzer, et al., 1980	LLK
15.42589	EVAL	Huber and Herzberg, 1979	LLK
16. ± 1.	EI	Farber and Srivastava, 1977	LLK
15.4	PI	Rabalais, Debies, et al., 1974	LLK
15.43	PE	Lee and Rabalais, 1974	LLK
15.42589 ± 0.00005	S	Herzberg and Jungen, 1972	LLK
15.4256 ± 0.0001	S	Takezawa, 1970	RDSH
15.38186 ± 0.00031	PE	Asbrink, 1970	RDSH
15.44 ± 0.01	EI	Lossing and Semeluk, 1969	RDSH
15.4256	S	Herzberg, 1969	RDSH
15.431 ± 0.022	TE	Villarejo, 1968	RDSH
15.439 ± 0.015	PE	Collin and Natalis, 1968	RDSH
15.43	CI	Cermak, 1968	RDSH
15.37 ± 0.05	EI	Kerwin, Marmet, et al., 1963	RDSH
15.4269 ± 0.0016	S	Beutler and Junger, 1936	RDSH

Appearance energy determinations

Ion	AE (eV)	Other Products	Method	Reference	Comment
H⁺	18.078 ± 0.003	H	PIPECO	Weitzel, Mahnert, et al., 1994	T = 0K; LL
H⁺	18.0 ± 0.2	H	EI	Crowe and McConkey, 1973	LLK
H⁺	17.28 ± 0.16	H^-	EI	Locht and Momigny, 1971	LLK
H⁺	17.3	H^-	EI	Curran, Laboratories	RDSH

De-protonation reactions

+ = Hydrogen

By formula: H^- + H⁺ = H₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	1675.3	kJ/mol	N/A	Shiell, Hu, et al., 2000	gas phase; Given: 139714.8±1 cm-1 at 0K, or 399.465±0.003 kcal/mol; B
Δ_rH°	1675.3	kJ/mol	N/A	Pratt, McCormack, et al., 1992	gas phase; 399.46±0.01 kcal/mol at 0K; 0.94 correction, Gurvich, Veyts, et al.; B
Δ_rH°	1675.3	kJ/mol	D-EA	Lykke, Murray, et al., 1991	gas phase; Reported: 6082.99±0.15 cm-1, or 0.754195(18) eV; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	1649.3 ± 0.42	kJ/mol	H-TS	Shiell, Hu, et al., 2000	gas phase; Given: 139714.8±1 cm-1 at 0K, or 399.465±0.003 kcal/mol; B
Δ_rG°	1649.3	kJ/mol	H-TS	Lykke, Murray, et al., 1991	gas phase; Reported: 6082.99±0.15 cm-1, or 0.754195(18) eV; B

References

Go To: Top, Gas phase thermochemistry data, Reaction thermochemistry data, Gas phase ion energetics data, Notes

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Cox, J.D.; Wagman, D.D.; Medvedev, V.A., CODATA Key Values for Thermodynamics, Hemisphere Publishing Corp., New York, 1984, 1. [all data]

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Hiraoka, K.; Kebarle, P., A Determination of the Stabilities of H5+, H7+, H9+, and H11+ from Measurement of the Gas Phase Ion Equilibria Hn+ + H2 = H(n + 2)+ (n = 3, 5, 7, 9), J. Chem. Phys., 1975, 62, 6, 2267, https://doi.org/10.1063/1.430751 . [all data]

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Pratt, S.T.; McCormack, E.F.; Dehmer, J.L.; Dehmer, P.M., Field-Induced Ion-Pair Formation in Molecular Hydrogen, Phys. Rev. Lett., 1992, 68, 5, 584, https://doi.org/10.1103/PhysRevLett.68.584 . [all data]

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Gurvich, L.V.; Veyts, I.V.; Alcock, C.B., Hemisphere Publishing, NY, 1989, V. 1 2, Thermodynamic Properties of Individual Substances, 4th Ed. [all data]

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Notes

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Symbols used in this document:

AE	Appearance energy
IE (evaluated)	Recommended ionization energy
S°_{gas,1 bar}	Entropy of gas at standard conditions (1 bar)
T	Temperature
Δ_rG°	Free energy of reaction at standard conditions
Δ_rH°	Enthalpy of reaction at standard conditions
Δ_rS°	Entropy of reaction at standard conditions

Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
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