I was wondering the weight of 1 liter of ethylene at 2000 bar and 310 Kelvin?

I have tried to just multiply the weight at 1 bar with 2000 but I don't think i got the correct answer because the answer I got was just below 2.4 kg per liter which seems way too high.

I calculated it with constant temperature.


1 Answer 1


If we treat it as an ideal gas, then \begin{aligned} PV &= n\mathcal{R}T \\ \mathcal{R} &=0.08314~\mathrm{L~bar~K^{-1}~mol^{-1}}\\ n &=\frac{PV}{\mathcal{R}T}=\frac{2000\cdot1}{0.08314\cdot310}=77.6~\mathrm{mol}\\ M(\ce{ethylene}) &=28~\mathrm{g~mol^{-1}}\\ \text{mass of ethylene} &= (28\cdot77.6) = 2.17~\mathrm{kg} \end{aligned}

Using the link[a] in the comment I find that the density of ethylene at $310~\mathrm{K}$ and $1800~\mathrm{bar}$ is $\varrho = 20.385~\mathrm{mol/L}$, and $\varrho = 21.065~\mathrm{mol/L}$ at $2200~\mathrm{bar}$. Averaging these two numbers gives an estimated density of $\varrho = 20.725~\mathrm{mol/L}$ at $310~\mathrm{K}$ and $2000~\mathrm{bar}$. So 1 liter of ethylene under these conditions would contain \begin{aligned} \varrho\cdot M_{\ce{C2H4}}\cdot V & ~= m_{\ce{C2H4}}\\ 20.725~\mathrm{\frac{mol}{L}} \cdot 28~\mathrm{\frac{g}{mol}}\cdot 1~\mathrm{L} & ~\approx 580~\mathrm{g}.\\ \end{aligned} Is that more in line with your expectations?

[a] Majid Jahangiri, Richard T Jacobsen, Richard B. Stewart and Robert D. McCarty: Thermodynamic Properties of Ethylene from the Freezing Line to 450 K at Pressures to 260 MPa. J. Phys. Chem. Ref. Data 1986, 15 (2), 593. (DOI:10.1063/1.555753) (mirror at www.nist.gov)

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    $\begingroup$ I like your answer, but I am curious if ethylene at $200~\mathrm{bar}$ is still a gas. (I would tend to liquid) Also I do not really think at these pressures any gas will behave ideal, probably not even helium. $\endgroup$ Jul 8, 2014 at 15:03
  • $\begingroup$ I thought about the gas-liquid question. Since a volume was given I went with gas. If it was liquid and we "assume" (I know) incompressibility - well it seemed too straightforward. But yes, whether a gas or a liquid, probably far from ideal. $\endgroup$
    – ron
    Jul 8, 2014 at 15:31
  • $\begingroup$ Here at work we have compressors that compress the gas to 2300 bars and the compressor can only handle 30% liquid so it is not a liquid, at least not in the sense that it can still be compressed but one of the engineers her found that there was something called "compressibility factor" which seem to have a lot of influence on the answer. $\endgroup$
    – Skretch
    Jul 8, 2014 at 15:34
  • $\begingroup$ Someone linked this link at the physics section of this site it has the answer $\endgroup$
    – Skretch
    Jul 8, 2014 at 15:41
  • $\begingroup$ If I take the molar density that is given in the tables on that site and multiply it by the molar weight of ethylene I get 28.05g/mol * 20.065 mol/dm^3 = 562.82325 g/dm^3 . This is at 310 K $\endgroup$
    – Skretch
    Jul 8, 2014 at 16:25

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