Ammonia (data page)

This page provides supplementary chemical data on ammonia.

Structure and properties

Molecular structure
Point group	C3v
Bond length	101.2 pm (N–H)[1]
Bond angle	106.7° (H–N–H)[1]
Bond strength	435 kJ/mol (H–NH2)
Crystal data
Crystal structure	?
Properties
Dipole moment	1.46 D
Dielectric constant	22 ε0 at 239 K
Magnetic susceptibility	diamagnetic
Acidity of NH4+ (pKa)	9.25

Thermodynamic properties

Phase diagram and crystalline states of ammonia
I. cubic, II. hcp, III. fcc, IV. orthorhombic

Phase behavior
Triple point	195.4 K (−77.75 °C), 6.060 kPa
Critical point	405.5 K (132.3 °C), 11.300 MPa
Std enthalpy change of fusion, ΔfusHo	+5.653 kJ/mol
Std entropy change of fusion, ΔfusSo	+28.93 J/(mol·K)
Std enthalpy change of vaporization, ΔvapHo	+23.35 kJ/mol at BP of −33.4 °C
Std entropy change of vaporization, ΔvapSo	+97.41 J/(mol·K) at BP of −33.4 °C
Solid properties
Std enthalpy change of formation, ΔfHosolid	? kJ/mol
Standard molar entropy, Sosolid	? J/(mol K)
Heat capacity, cp	? J/(mol K)
Liquid properties
Std enthalpy change of formation, ΔfHoliquid	−80.882 ± 0.053 kJ/mol[2]
Standard molar entropy, Soliquid	? J/(mol K)
Heat capacity, cp	80.80 J/(mol K)
Gas properties
Std enthalpy change of formation, ΔfHogas	−45.556 ± 0.029 kJ/mol[3]
Std Gibbs free energy change of formation, ΔfGogas	−16.6 kJ/mol
Standard molar entropy, Sogas	192.77 J/(mol K)
Heat capacity, cp	35.06 J/(mol K)
Heat capacity ratio, γ at 15 °C	1.310
van der Waals' constants	a = 422.5 L2 kPa/mol2 b = 0.03707 L/mol

Vapor–liquid equilibrium data

P in mm Hg		1	10	40	100	400	760	1520	3800	7600	15600	30400	45600
T in °C		−109.1(s)	−91.9(s)	−79.2(s)	−68.4	−45.4	−33.6	−18.7	4.7	25.7	50.1	78.9	98.3

Table data (above) obtained from CRC Handbook of Chemistry and Physics 44th ed. The (s) notation indicates equilibrium temperature of vapor over solid. Otherwise temperature is equilibrium of vapor over liquid.

log₁₀ of anhydrous ammonia vapor pressure. Uses formula shown below.

Vapor-pressure formula for ammonia:^[4]

log₁₀P = A – B / (T − C),

where P is pressure in kPa, and T is temperature in kelvins;

A = 6.67956, B = 1002.711, C = 25.215 for T = 190 K through 333 K.

Vapor over anhydrous ammonia[5] Temp. Pressure ρ of liquid ρ of vapor ΔvapH −78 °C 5.90 kPa −75 °C 7.93 kPa 0.73094 g/cm3 7.8241×10−5 g/cm3 −70 °C 10.92 kPa 0.72527 g/cm3 1.1141×10−4 g/cm3 −65 °C 15.61 kPa 0.71953 g/cm3 1.5552×10−4 g/cm3 −60 °C 21.90 kPa 0.71378 g/cm3 2.1321×10−4 g/cm3 −55 °C 30.16 kPa 0.70791 g/cm3 2.8596×10−4 g/cm3 −50 °C 40.87 kPa 0.70200 g/cm3 3.8158×10−4 g/cm3 1417 J/g −45 °C 54.54 kPa 0.69604 g/cm3 4.9940×10−4 g/cm3 1404 J/g −40 °C 71.77 kPa 0.68999 g/cm3 6.4508×10−4 g/cm3 1390 J/g −35 °C 93.19 kPa 0.68385 g/cm3 8.2318×10−4 g/cm3 1375 J/g −30 °C 119.6 kPa 0.67764 g/cm3 1.0386×10−3 g/cm3 1361 J/g −25 °C 151.6 kPa 0.67137 g/cm3 1.2969×10−3 g/cm3 1345 J/g −20 °C 190.2 kPa 0.66503 g/cm3 1.6039×10−3 g/cm3 1330 J/g −15 °C 236.3 kPa 0.65854 g/cm3 1.9659×10−3 g/cm3 1314 J/g −10 °C 290.8 kPa 0.65198 g/cm3 2.3874×10−3 g/cm3 1297 J/g −5 °C 354.8 kPa 0.64533 g/cm3 2.8827×10−3 g/cm3 1280 J/g  0 °C 429.4 kPa 0.63857 g/cm3 3.4528×10−3 g/cm3 1263 J/g  5 °C 515.7 kPa 0.63167 g/cm3 4.1086×10−3 g/cm3 1245 J/g  10 °C 614.9 kPa 0.62469 g/cm3 4.8593×10−3 g/cm3 1226 J/g  15 °C 728.3 kPa 0.61755 g/cm3 5.7153×10−3 g/cm3 1207 J/g  20 °C 857.1 kPa 0.61028 g/cm3 6.6876×10−3 g/cm3 1187 J/g  25 °C 1003 kPa 0.60285 g/cm3 7.7882×10−3 g/cm3 1167 J/g  30 °C 1166 kPa 0.59524 g/cm3 9.0310×10−3 g/cm3 1146 J/g  35 °C 1350 kPa 0.58816 g/cm3 1.0431×10−2 g/cm3 1124 J/g  40 °C 1554 kPa 0.57948 g/cm3 1.2006×10−2 g/cm3 1101 J/g  45 °C 1781 kPa 0.57130 g/cm3 1.3775×10−2 g/cm3 1083 J/g  50 °C 2032 kPa 0.56287 g/cm3 1.5761×10−2 g/cm3 1052 J/g  55 °C 2310 kPa 0.55420 g/cm3  60 °C 2613 kPa 0.54523 g/cm3 2.05×10−2 g/cm3  65 °C 2947 kPa 0.53596 g/cm3  70 °C 3312 kPa 0.52632 g/cm3 2.65×10−2 g/cm3  75 °C 3711 kPa 0.51626 g/cm3  80 °C 4144 kPa 0.50571 g/cm3 3.41×10−2 g/cm3  85 °C 4614 kPa 0.49463 g/cm3  90 °C 5123 kPa 0.48290 g/cm3 4.39×10−2 g/cm3  95 °C 5672 kPa 0.47041 g/cm3 100 °C 6264 kPa 0.45693 g/cm3 5.68×10−2 g/cm3 Temp. Pressure ρ of liquid ρ of vapor ΔvapH The table above gives properties of the vapor–liquid equilibrium of anhydrous ammonia at various temperatures. The second column is vapor pressure in kPa. The third column is the density of the liquid phase. The fourth column is the density of the vapor. The fifth column is the heat of vaporization needed to convert one gram of liquid to vapor.

Freezing curve of ammonia-water system. Three eutectic points I. II. and III. are shown. Left of the I. point the frozen component is ice. Right of the III. point the frozen component is ammonia.[6] Vapor over aqueous ammonia solution[7] Temp. %wt NH3 Partial pressure NH3 Partial pressure H2O 0 °C 4.72 1.52 kPa 0.68 kPa 9.15 3.31 kPa 0.71 kPa 14.73 6.84 kPa 0.55 kPa 19.62 11.0 kPa 0.40 kPa 22.90 14.9 kPa 0.37 kPa 10 °C 4.16 2.20 kPa 1.21 kPa 8.26 4.96 kPa 1.17 kPa 12.32 8.56 kPa 1.01 kPa 15.88 12.68 kPa 0.93 kPa 20.54 19.89 kPa 0.83 kPa 21.83 22.64 kPa 0.73 kPa 19.9 °C 4.18 3.65 kPa 2.19 kPa 6.50 6.11 kPa 2.15 kPa 6.55 6.13 kPa 2.13 kPa 7.72 7.49 kPa 2.08 kPa 10.15 10.75 kPa 2.01 kPa 10.75 11.51 kPa 1.96 kPa 16.64 22.14 kPa 1.72 kPa 19.40 28.74 kPa 1.64 kPa 23.37 40.32 kPa 1.37 kPa 30.09 °C 3.93 5.49 kPa 4.15 kPa 7.43 11.51 kPa 3.89 kPa 9.75 16.00 kPa 3.80 kPa 12.77 23.33 kPa 3.55 kPa 17.76 38.69 kPa 3.31 kPa 17.84 38.81 kPa 3.24 kPa 21.47 53.94 kPa 2.95 kPa 40 °C 3.79 8.15 kPa 7.13 kPa 7.36 17.73 kPa 6.76 kPa 11.06 29.13 kPa 6.55 kPa 15.55 47.14 kPa 5.52 kPa 17.33 57.02 kPa 20.85 76.81 kPa 5.04 kPa 50 °C 3.29 10.54 kPa 11.95 kPa 5.90 20.17 kPa 11.61 kPa 8.91 32.88 kPa 11.07 kPa 11.57 45.56 kPa 10.75 kPa 14.15 60.18 kPa 10.27 kPa 14.94 64.94 kPa 10.03 kPa 60 °C 3.86 18.25 kPa 19.21 kPa 5.77 28.78 kPa 7.78 40.05 kPa 18.47 kPa 9.37 50.09 kPa 18.07 kPa 9.37 63.43 kPa 17.39 kPa Temp. %wt NH3 Partial Pressure NH3 Partial Pressure H2O

Heat capacity of liquid and vapor

Heat capacity, cp, of anhydrous ammonia gas. Uses polynomial obtained from CHERIC.[8]

Heat capacity of anhydrous liquid ammonia. Uses polynomial obtained from CHERIC.[8]

Spectral data

UV-Vis
λmax	None nm
Extinction coefficient, ε	None
IR
Major absorption bands	3444, 3337, 1627, 950 cm−1
NMR
Proton NMR
Carbon-13 NMR	None – no carbons
Other NMR data
MS
Masses of main fragments	17 (100%) 16(80%) 15(9%)

Regulatory data

Regulatory data
EINECS number	231-635-3 (gas) 215-647-6 (soln.)
EU index number	007-001-00-5 (gas) 007-001-01-2 (soln.)
PEL-TWA (OSHA)	50 ppm (35 mg/m3)
IDLH (NIOSH)	300 ppm
Flash point	11 °C
Autoignition temperature	651 °C
Explosive limits	15–28%
RTECS #	BO0875000

Safety data sheet

The handling of this chemical may incur notable safety precautions... It is highly recommend that you seek the Safety Data Sheet (SDS) for this chemical from a reliable source and follow its directions.

• SIRI
• Science Stuff (Ammonia Solution)