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Lowest adiabatic index

  1. Jun 6, 2014 #1

    to the best of your knowledge, what is

    1) the gas with the lowest adiabatic index ##\gamma=\frac{c_p}{c_v}## at room temperature
    2) a very common, non-flammable, non-toxic gas with the lowest adiabatic index at room temperature

    Many thanks
  2. jcsd
  3. Jun 8, 2014 #2


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    In general, you're looking for molecules with the largest number of atoms. Octafluoropropane, also called Freon 218, has a ratio of specific heats of ~1.066 at room temperature and atmospheric pressure. Regarding toxicity, check the MSDS.
  4. Jun 8, 2014 #3
    Just dug out the old thermo book...300 K and 1 ATM

    Butane 1.091
    Octane 1.044
    Propane 1.126
    Ethane 1.186

    Those are the lowest ratios I found, not sure on toxicity though. However, I'm gonna guess they're a heck of a lot less toxic than anything with Chlorine or Flourine in it...
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