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:
ChemEurope
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 |
| Author: | BPL |