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# Molecular Weight of Substances

The molecular weight of a substance, also called the molar mass , M, is the mass of 1 mole of that substance, given in M gram.

In the SI system the unit of M is [kg/kmol] and in the English system the unit is [lb/lbmol], while in the cgs system the unit of M is [g/mol]. Molecular weight is represented by the same number in all unit systems regardless of the system used. For this reason, in many cases the unit for the molecular weight is not mentioned; however, one must realize that it is not a dimensionless parameter.

The molecular weight of a pure compound is determined from its chemical formula and the atomic weights of its elements. The atomic weights of the elements found in organic substances are C = 12.011, H = 1.008, S = 32.065, O = 15.999, and N = 14.007.

Example: The molecular weight of ethanol (C2H5 OH)
To calculate the molecular weight of ethanol, the molecular weight of each atom in the molecule is summed:

M ethanol = 2*12.011[kg/kmol] + 6*1.008[kg/kmol] + 1*15.999 [kg/kmol] = 46.069 [kg/kmol]

Molecular Weight of Substances
Substance

Molecular Weight
[kg/kmol]
[g/mol]
[lb/lbmol]

Acetylene, C2H 2 26.038
Air 28.966
Ammonia (R-717) 17.02
Argon, Ar 39.948
Benzene 78.114
n - Butane, C 4 H 10 58.124
1-Butene 56.108
cis -2-Butene 56.108
trans-2-Butene 56.108
Butylene 56.06
Carbon Dioxide, CO 2 44.01
Carbon Disulphide 76.13
Carbon Monoxide, CO 28.011
Chlorine 70.906
Cyclohexane 84.162
Cyclopentane 70.135
n - Decane 142.286
Deuterium 2.014
2,3 - Dimetylbutane 86.178
2,2 - Dimethylpentane 100.205
Diisobutyl 114.232
Duoderane 170.21
Ethane, C2H6 30.070
Ethene 28.05
Ethyl Alcohol 46.07
Ethylbenzene 106.168
Ethyl Chloride 64.515
3 - Ethylpentane 100.205
Ethylene, C2H 4 28.054
Fluorine 37.996
Helium, He 4.002602
n - Heptane 100.205
n - Hexane 86.178
Hydrochloric Acid 36.47
Hydrogen, H 2 2.016
Hydrogen Chloride 36.461
Hydrogen Sulfide 34.076
Hydroxyl, OH 17.01
Isobutane (2-Metyl propane) 58.124
Isobutene 56.108
Isooctane 210.63
Isopentane 72.151
Isoprene 68.119
Isopropylbenzene 120.195
Krypton 83.80
Methane, CH 4 16.043
Methyl Alcohol 32.04
Methyl Butane 72.15
Methyl Chloride 50.488
Methylcyclohexane 98.189
Methylcyclopentane 84.162
2 - Methylhexane 100.205
2 - Methylpentane 86.178
Natural Gas 19.00
Neon, Ne 20.179
Neohexane 86.178
Neopentane 72.151
Nitric Oxide, NO 30.006
Nitrogen, N 2 28.0134
Nitrous Oxide, N2O 44.013
n - Nonane 128.259
n - Octane 114.232
Oxygen, O 2 31.9988
Ozone 47.998
n - Pentane 72.151
Pentylene 70.08
Propane, C3 H 8 44.097
Propene 42.081
Propylene 42.08
R-11 137.37
R-12 120.92
R-22 86.48
R-114 170.93
R-123 152.93
R-134a 102.03
R-611 60.05
Styrene 104.152
Sulfur 32.02
Sulfur Dioxide (Sulphur Dioxide) 64.06
Sulfuric Oxide 48.1
Toluene, toluol 92.141
Triptane 100.205
Xenon 131.30
o - Xylene, xylol 106.168
Water Vapor - Steam, H2O 18.02

## Related Topics

### • Material Properties

Properties of gases, fluids and solids. Densities, specific heats, viscosities and more.

## Related Documents

### Acetone - Thermophysical Properties

Chemical, physical and thermal properties of acetone, also called 2-propanone, dimethyl ketone and pyroacetic acid. Phase diagram included.

### Air - Molecular Weight and Composition

Dry air is a mixture of gases where the average molecular weight (or molar mass) can be calculated by adding the weight of each component.

### Benzene - Thermophysical properties

Chemical, physical and thermal properties of benzene, also called benzol. Phase diagram included.

### Butane - Thermophysical Properties

Chemical, physical and thermal properties of n-Butane.

### Carbon dioxide - Prandtl Number vs. Temperature and Pressure

Figures and table with changes in Prandtl number for carbon dioxide with changes in temperature and pressure.

### Carbon Dioxide - Thermophysical Properties

Chemical, physical and thermal properties of carbon dioxide. Phase diagram included.

### Compression and Expansion of Gases

Isothermal and isentropic gas compression and expansion processes.

### Ethylene - Thermophysical Properties

Chemical, physical and thermal properties of ethylene, also called ethene, acetene and olefiant gas. Phase diagram included.

### Fuel Gases - Flame Temperatures

Adiabatic flame temperatures for common fuel gases - propane, butane, acetylene and more - in air or oxygen atmospheres.

### Gases - Densities

Densities and molecular weights of common gases like acetylene, air, methane, nitrogen, oxygen and others.

### Gases - Explosion and Flammability Concentration Limits

Flame and explosion limits for gases like propane, methane, butane, acetylene and more.

### Gases - Molar Specific Heats

Molar specific heats for some common gases at constant volume.

### Gases - Specific Gravities

Specific gravities of air, ammonia, butadiene, carbon dioxide, carbon monoxide and some other common gases.

### Gases - Specific Heats and Individual Gas Constants

Specific heat at constant volume, specific heat at constant pressure, specific heat ratio and individual gas constant - R - common gases as argon, air, ether, nitrogen and many more.

### Hydrocarbons - Melting Point vs. Molecular Weight

Calculate melting point of hydrocarbons from molecular weight (molar mass).

### Hydrocarbons - Vapor Pressures

Vapor pressure vs. temperature for propane, n-butane, n-heptane and n-pentane hydrocarbons.

### Hydrogen - Thermophysical Properties

Chemical, Physical and Thermal Properties of Hydrogen - H2.

### Methane - Thermophysical Properties

Chemical, Physical and Thermal Properties of Methane - CH4. Phase diagram included.

### Moist Air - Mole Fraction of Water Vapor

Mole fraction of water vapor is the ratio of water molecules to air and water molecules.

### Mole and the Avagadro's Number

The mole is the SI base unit for an amount of a substance.

### Total and Partial Pressure - Dalton's Law of Partial Pressures

How to calculate total pressure and partial pressures for gas mixtures from Ideal Gas Law.

### Vapor and Steam

An introduction to vapor and steam.

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