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What pressure does liquid nitrous oxide need at −45 °C to remain liquid? How can I calculate its pressure required for other temperatures?

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    $\begingroup$ Rather read from phase diagram then calculate, unless you find curve fitting equation. $\endgroup$
    – Mithoron
    Mar 22 '21 at 23:24
  • $\begingroup$ @Mithoron Would you point me to a phase diagram to read this from? I could really not find a decent one. $\endgroup$
    – Kozuch
    Mar 22 '21 at 23:43
  • $\begingroup$ I also found a bad one... $\endgroup$
    – Mithoron
    Mar 22 '21 at 23:55
  • $\begingroup$ «Nitrous oxide: Saturation properties and the phase diagram», Ferreira, Lobo, The Journal of Chemical Thermodynamics, 41, 2009, 1394-1399, doi 10.1016/j.jct.2009.06.017, seems to cover the range you need here. $\endgroup$
    – Buttonwood
    Mar 23 '21 at 6:15
  • $\begingroup$ If such a diagram was not available, or for other compound, one could use the knowledge of the boiling point, the evaporation molar enthalpy (or its approximation by the empirical rule ( forgot the rule name ) saying evaporation molar entropy change is 90 J/K/mol and the Clausius-Clapeyron equation.) Then it is possible to compute the approximation of the curve p_vap = f(T) $\endgroup$
    – Poutnik
    Mar 23 '21 at 7:03
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Using NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP) – NIST Standard Reference Database 23, Version 9, I found the saturation point of nitrous oxide at equilibrium for a temperature of $T=-45.000\ \mathrm{^\circ C}$ at a pressure of $p=783110\ \mathrm{Pa}=7.8311\ \mathrm{bar}$; for $T=-78.000\ \mathrm{^\circ C}$, it is $p=182290\ \mathrm{Pa}=1.8229\ \mathrm{bar}$.

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    $\begingroup$ Thank you very much! I was about to ask if there may be a (freely accessible) online database/calculator where one could get this info and I just found this REFPROP version 10 is selling for $325 here: nist.gov/srd/refprop I guess you have purchased that, right? Would you mind looking up one more value - pressure for -78°C? Thanks! $\endgroup$
    – Kozuch
    Mar 23 '21 at 19:48
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    $\begingroup$ Looks like there is an alternative to REFPROP - it is called CoolProp. Not very user friendly though. Website: coolprop.org $\endgroup$
    – Kozuch
    Mar 23 '21 at 20:06

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