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The planet in question is this one. The atmosphere mainly consists of nitrogen and is approximately a quarter the density of Earth's; I chose surface temperatures ranging from -50°C to 0°C.

I need a compount which effectively "replaces" water on this planet. Any compounds similar to Water in their composition and their chemical reactions, with oxygen replaced by nitrogen, are welcome; I looked up Azanide (H2N) but could not find information about its chemical and physical properties.

A modification of the surface temperature is allowed, which means that compounds with evaporation temperatures between -100°C and -50°C are permitted too. The difference between the melting and evaporation temperature must be as big as possible.

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  • $\begingroup$ I doubt if azanide would be a replacement for H2) (water) as this web page suggests it is a molecular subunit of proteins and other complex molecules: wikigenes.org/e/chem/e/2826723.html $\endgroup$
    – a4android
    Mar 3, 2017 at 12:35
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    $\begingroup$ FWIW, earth's atomosphere is 78% gaseous nitrogen already. I'd call that "mainly nitrogen". You're going to need to come up with a good reason why the (relatively stable) diatomic nitrogen would be found in other forms. $\endgroup$
    – papidave
    Mar 4, 2017 at 15:56

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Replacing Oxygen with Nitrogen pretty much gets away all the reasons for the peculiar properties of water: highly polar molecule with strong H bonds between molecules, resulting in its relatively high boiling point.

The closest small molecule is ammonia, NH3, which melts at -78 °C and boils at -33 °C. In your indicated temperature range you could have seas of ammonia and gas, but no solid ammonia.

But your planet is less dense, therefore it will have a lower gravity if the size is similar to Earth. A lower gravity means a lower pressure, and therefore you can wave goodbye to your liquid ammonia.

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  • $\begingroup$ Looked up a phase diagram. cpp.edu/~skboddeker/122/exam/122-07-4fall-e2_files/image005.jpg $\endgroup$ Mar 4, 2017 at 14:14
  • $\begingroup$ The highly polar nature of water isn't simply useful because of its influence on melting and boiling points; It also makes water useful as a solvent for a variety of ionic and polar molecules. It also causes ice to be (unlike most materials) less dense as a solid than as a liquid. Ice floats, which allows us to have seas with ice on top that stay mostly liquid. $\endgroup$
    – papidave
    Mar 4, 2017 at 15:51
  • $\begingroup$ Lower gravity does not necessarily imply lower pressure. Titan has much lower gravity than Earth, and higher surface pressure. Venus has slightly lower gravity, and much higher surface pressure. $\endgroup$ Nov 12, 2019 at 18:43

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