Molecular weight¶

Functions to calculate molecular weight of an element, compound, or gas mixture. Note that mole fractions must sum to one otherwise an error is raised.

chemics.molecular_weight.mw(formula)[source]

Tokenize a molecular formula to determine total molecular weight. Calculation is based on atomic weight values from IUPAC 1.

Parameters

formula (str) – Molecular formula or element.

Returns

mw (float) – Molecular weight of the formula or element [g/mol]

Examples

>>> mw('C')
12.011

>>> mw('CH4')
16.04

>>> mw('(NH4)2SO4')
132.13


References

1

IUPAC Periodic Table of the Elements. International Union of Pure and Applied Chemistry, 2016. https://iupac.org/what-we-do/periodic-table-of-elements/.

chemics.molecular_weight.mw_mix(mws, xs)[source]

Molecular weight of a gas mixture calculated as a weighted mean.

Parameters
• mws (list, tuple, or array) – Molecular weight of each gas component [g/mol]

• xs (list, tuple, or array) – Mole fraction of each gas component [-]

Returns

mw_mix (float) – Molecular weight of a gas mixture [g/mol]

Raises

ValueError – If sum of mole fractions does not equal 1.0

Examples

>>> mw_h2 = cm.mw('H2')
... mw_n2 = cm.mw('N2')
... mw_mix([mw_h2, mw_n2], [0.8, 0.2])
7.2156

>>> mw_h2 = cm.mw('H2')
... mw_n2 = cm.mw('N2')
... mw_ch4 = cm.mw('CH4')
... mw_mix([mw_h2, mw_n2, mw_ch4], [0.4, 0.1, 0.5])
11.6293