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Ammonia - Thermophysical Properties

Chemical, Physical and Thermal Properties of Ammonia. Phase diagram included.

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Ammonia is a colourless gas with a characteristic pungent smell and hazardous in its concentrated form.

Chemical, physical and thermal properties of Ammonia, NH3:
Values at 25oC /77oF / 298 K and 1 atm., if not other temperature and pressure given.
If values are given for liquid ammonia at ambient temperature, the ammonia is pressurized above 1 atm.

Property Value Unit Value Unit Value Unit Value Unit
Acidity (pKa) 9.24
Acidity (pKa) at -33°C 32.5
Autoignition point 903 K 630 °C 1166 °F
Basicity (pKb) 4.75
Boiling point 239.82 K -33.33 °C -27.99 °F
Critical density 14327 mol/m3 243.99 kg/m3 15.23 lb/ft3 0.4734 slug/ft3
Critical pressure 11.357 MPa=MN/m2 113.57 bar 112.08 atm 1647.2 psi=lbf/in2
Critical temperature 405.56 K 132.41 °C 270.34 °F
Critical volume 69.8 cm3/mol 0.00410 m3/kg 0.0657 ft3/lb 2.11 ft3/slug
Density, gas 41.1 mol/m3 0.699 kg/m3 0.0437 lb/ft3 0.00136 slug/ft3
Density, liquid at -28 °F/-33.35°C, 1 atm 40868 mol/m3 696 kg/m3 43.4 lb/ft3 1.35 slug/ft3
Density, liquid at 70 °F/21.1°C 36259 mol/m3 617.5 kg/m3 38.55 lb/ft3 1.198 slug/ft3
Flammable no
Flash point 405 K 132 °C 269 °F
Gas constant, R 488.2 J/kg K 0.1356 Wh/(kg K) 90.74 ft lbf/lb °R 2919 ft lbf/slug °R
Gibbs free energy of formation, ΔGf -16.6 kJ/mol -975 kJ/kg -0.42 Btu/lb
Heat (enthalpy) of combustion, ΔHc (gas) 382.8 kJ/mol 22477 kJ/kg 9.663 Btu/lb
Heat (enthalpy) of evaporation, ΔHv, at boiling point 23.37 kJ/mol 1372.0 kJ/kg 589.87 Btu/lb
Heat(enthalpy) of formation, ΔHf (gas) -45.9 kJ/mol -2695 kJ/kg -1.16 Btu/lb
Heat (enthalpy) of fusion/melting, ΔHm 5.653 kJ/mol 332.3 kJ/kg 143 Btu/lb
Heat (enthalpy) of sublimation, ΔHS, at 180 K 31.2 kJ/mol 1832 kJ/kg 0.79 Btu/lb
Ionization potential 10.18 eV
Melting (freezing) point 195.42 K -77.73 °C -107.91 °F
Molecular Weight 17.03052 g/mol 0.03755 lb/mol
pH of 0.01 N aqueous solution 10.6
pH of 0.1 N aqueous solution 11.1
pH of 1.0 N aqueous solution 11.6
Standard molar entropy, S° (gas) at 1 bar 192.77 J/mol K 11.32 kJ/kg K 0.002704 Btu/lb °F
Solubility in water, at 20°C 540 mg/ml
Solubility in water, at 24°C 482 mg/ml
Sound velocity in gas 415 m/s
Specific Gravity, gas (density relativ to air) 0.604
Specific heat (heat capacity), Cp (gas) 37.0 J/mol K 2.175 kJ/kg K 0.5200 Btu/lb°F
= cal/g K
Specific heat (heat capacity), Cp (liquid) 80.8 J/mol K 4.744 kJ/kg K 1.133 Btu/lb°F
= cal/g K
Specific heat ratio - Cp/Cv (gas) 1.32
Specific volume 0.02435 m3/mol 1.43 m3/kg 22.91 ft3/lb 736.99 ft3/slug
Surface tension at 11.1°C/52.0°F 23.4 dynes/cm
Surface tension at 34.1°C/93.4°F 18.1 dynes/cm
Thermal Conductivity 0.026 W/m°C 0.015 Btu/hr ft °F
Triple point pressure 0.00609 MPa=MN/m2 0.0609 bar 0.0601 atm 0.883 psi=lbf/in2
Triple point temperature 195.5 K -77.65 °C -107.77 °F
Vapor (saturation) pressure 1.00 MPa=MN/m2 7500 mm Hg 9.869 atm 145.0 psi=lbf/in2
Vapor (saturation) pressure at -49.72°F/-45.4°C 0.0533 MPa=MN/m2 400 mm Hg 0.526 atm 7.73 psi=lbf/in2
Viscosity, dynamic (absolute) (gas) 0.0100 cP 6.72*10-6 lbm/ft s 0.209*10-6 lbf s/ft2
Viscosity, dynamic (absolute) at 27°C (liq) 0.1293 cP 86.89*10-6 lbm/ft s 2.70*10-6 lbf s/ft2
Viscosity, dynamic (absolute) at -33.5°C (liq) 0.255 cP 171.4*10-6 lbm/ft s 5.326*10-6 lbf s/ft2

See also the following documents for changes in ammonia properties with changes in pressure and temperature:

Ammonia is a gas at standard conditions. However, at low temperature and/or high pressures the gas becomes a liquid. The phase diagram for ammonia shows the phase behavior with changes in temperature and pressure. The curve between the triple point and the critical point shows the ammonia boiling point with changes in pressure.

Below the triple point temperature, ammonia becomes a solid, this phase will also be present at very high pressure (> 10 000 bar) and ambient temperature.

/Ammonia phase diagram C

At the critical point there is no change of state when pressure is increased or if heat is added.

The triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.

See also more about atmospheric pressure, and STP - Standard Temperature and Pressure & NTP - Normal Temperature and Pressure, as well as Thermophysical properties of:
Acetone,  AcetyleneAirArgon, Butane, Carbon dioxide, Carbon monoxide, Ethane, Ethanol, Helium, Hydrogen, Methane, MethanolNitrogen, Oxygen, Propane, Water and Heavy water, D2O.

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