Gas Database

(c) 2008 by Barton Paul Levenson

The table belows lists names, chemical symbols, molecular weights, and constant-pressure specific heat for several gases found in planetary atmospheres. This information is valuable for a wide variety of atmospheric calculations. I do a lot of stuff with planetary atmospheres, and I just got tired of searching through google entries whenever I needed a figure. Thus...

The units of molecular weight are Atomic Mass Units (AMUs), the latest value of one AMU being (according to NIST/CODATA), 1.660538782 x 10-27 kg. The units of specific heat are Joules per Kelvin per kilogram (J K-1 kg-1). Thanks to Rod B., a RealClimate poster, who pointed out the desirability of specifying units.

Gas Formula Molecular Weight Specific Heat
Ammonia NH3 17.0305  2190
Argon Ar 39.9480   520
Carbon Dioxide CO2 44.0098   844
Carbon Monoxide CO 28.0110  1020
Ethane C2H6 30.0696  1750
Ethylene C2H4 28.0538  1530
Helium He  4.0026  5193
Hydrogen H2  2.0159 14320
Hydrogen Chloride HCl 36.4609   800
Krypton Kr 83.8000   248
Methane CH4 16.0428  2220
Neon Ne 20.1790  1030
Nitrogen N2 28.0134  1040
Nitrous Oxide N2O 44.0129   880
Oxygen O2 31.9988   919
Ozone O3 47.9982   818
Propane C3H8 44.0965  1670
Propene/Propylene C3H6 42.0806  1500
Sulfur Dioxide SO2 64.0648   640
Water Vapor H2O 18.0153  1930

Source for molecular weights:

Source for specific heats:
The Engineering Toolbox

Also miscellaneous web sources--had to go to Wikipedia for krypton, and as for ozone, forget about it--I searched for half an hour before I found a google books textbook that listed a figure. Good grief, people, if you're going to write about ozone, what's wrong with listing it's heat capacity?

Note added 11/11/2009: My original figures for Helium and Krypton (519 and 20,786 J K-1 kg-1, respectively) were grossly wrong--hear that, Wikipedia?. I studied thermodynamic chem texts and found there was actually a formula for cp. There are problems with the formula--it depends on a quantity called the "number of degrees of freedom" for the molecule which is hard to predict, and it only gives figures appropriate for standard temperature and pressure (273.16 K and 101,300 Pa respectively). But the figures are usually not very far off, and the ones for Helium and Krypton were way, WAY different than what I had. So I substituted the figures from the formula above.

Helium was apparently a typo in my original source ("519" which it should have been "5193"). I have NO IDEA where the bizarrely inflated figure for Krypton came from. But it never looked right to me, which is why I hit the books and found the formula in the first place. Common sense should have helped--it's clear from the table that cp tends to go down with molecular weight. Light helium shouldn't have had such a small figure; heavy Krypton shouldn't have had such a large one.

Live and learn.

Page created:11/27/2008
Last modified:  11/07/2012