# Ammonia - Thermophysical Properties

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

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

Chemical, physical and thermal properties of Ammonia, NH_{3}:

Values at 25^{o}C /77^{o}F / 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.

For full table with Imperial units -** rotate the screen!**

Property |
Value |
Unit |
Value |
Unit |
Value |
Unit |
Value |
Unit |
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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/m^{3} |
243.99 | kg/m^{3} |
15.23 | lb/ft^{3} |
0.4734 | ^{}slug/ft^{3} |
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Critical pressure | 11.357 | MPa=MN/m^{2} |
113.57 | bar | 112.08 | atm | 1647.2 | psi=lbf/in^{2} |
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Critical temperature | 405.56 | K | 132.41 | °C | 270.34 | °F | |||||

Critical volume | 69.8 | cm^{3}/mol |
0.00410 | m^{3}/kg |
0.0657 | ft^{3}/lb |
2.11 | ft^{3}/slug |
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Density, gas | 41.1 | mol/m^{3} |
0.699 | kg/m^{3} |
0.0437 | lb/ft^{3} |
0.00136 | slug/ft^{3} |
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Density, liquid at -28 °F/-33.35°C, 1 atm | 40868 | mol/m^{3} |
696 | kg/m^{3} |
43.4 | lb/ft^{3} |
1.35 | slug/ft^{3} |
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Density, liquid at 70 °F/21.1°C | 36259 | mol/m^{3} |
617.5 | kg/m^{3} |
38.55 | lb/ft^{3} |
1.198 | slug/ft^{3} |
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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 lb_{f}/lb °R |
2919 | ft lb_{f}/slug °R |
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Gibbs free energy of formation, ΔG_{f} |
-16.6 | kJ/mol | -975 | kJ/kg | -0.42 | Btu/lb | |||||

Heat (enthalpy) of combustion, ΔH_{c} (gas) |
382.8 | kJ/mol | 22477 | kJ/kg | 9.663 | Btu/lb | |||||

Heat (enthalpy) of evaporation, ΔH_{v}, at boiling point |
23.37 | kJ/mol | 1372.0 | kJ/kg | 589.87 | Btu/lb | |||||

Heat(enthalpy) of formation, ΔH_{f }(gas) |
-45.9 | kJ/mol | -2695 | kJ/kg | -1.16 | Btu/lb | |||||

Heat (enthalpy) of fusion/melting, ΔH_{m} |
5.653 | kJ/mol | 332.3 | kJ/kg | 143 | Btu/lb | |||||

Heat (enthalpy) of sublimation, ΔH_{S}, 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 |
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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 - C_{p}/C_{v} (gas) |
1.32 | ||||||||||

Specific volume | 0.02435 | m^{3}/mol |
1.43 | m^{3}/kg |
22.91 | ft^{3}/lb |
736.99 | ft^{3}/slug |
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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/m^{2} |
0.0609 | bar | 0.0601 | atm | 0.883 | psi=lb_{f}/in^{2} |
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Triple point temperature | 195.5 | K | -77.65 | °C | -107.77 | °F | |||||

Vapor (saturation) pressure | 1.00 | MPa=MN/m^{2} |
7500 | mm Hg | 9.869 | atm | 145.0 | psi=lb_{f}/in^{2} |
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Vapor (saturation) pressure at -49.72°F/-45.4°C | 0.0533 | MPa=MN/m^{2} |
400 | mm Hg | 0.526 | atm | 7.73 | psi=lb_{f}/in^{2} |
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Viscosity, dynamic (absolute) (gas) | 0.0100 | cP | 6.72*10-6 | lbm/ft s | 0.209*10-6 | lb_{f} s/ft^{2} |
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Viscosity, dynamic (absolute) at 27°C (liq) | 0.1293 | cP | 86.89*10-6 | lbm/ft s | 2.70*10-6 | lb_{f} s/ft^{2} |
|||||

Viscosity, dynamic (absolute) at -33.5°C (liq) | 0.255 | cP | 171.4*10-6 | lbm/ft s | 5.326*10-6 | lb_{f} s/ft^{2} |

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

- Density at varying temperature and pressure
- Dynamic and Kinematic Viscosity
- Liquid Ammonia - Thermal Properties at Saturation Pressure
- Prandtl number
- Properties at Gas-Liquid Equilibrium Conditions
- Specific heat
- Thermal Conductivity at Varying Temperature and Pressure
- Vapour Pressure at gas-liquid 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, Acetylene, Air, Argon, Benzene, Butane, Carbon dioxide, Carbon monoxide, Ethane, Ethanol, Ethylene, Helium, Hydrogen, Hydrogen sulfide, Methane, Methanol, Nitrogen, Oxygen, Pentane, Propane, Toluene, Water and Heavy water, D_{2}O.

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.

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.