Help with chemistry details

2014-08-28T00:52:31-04:00

So off the winds of a short story competition I am starting another short story (fingers crossed no writers block)

One of the details I have not worked out is for the planet it takes place on. I wanted a world where the 'land' is ice (ie frozen water) and the oceans were some other liquid that boils lower than 0 degrees Celsius.

Whatever this element or compound is I would like to be above -183 degrees (as i believe that is the boiling point of oxygen, i still want the humans there to be able to breathe haha)

i would also like this liquid to be toxic to humans (if they fall in the ocean or a mist of it rolls by they have to put on masks), but there are low enough amounts of it in the air that normally a mask is not needed for a ig unit.

im not too good with the chemistry so I appreciate any help from those that might be! i have looked up carbon dioxide and i think that that works. the oceans can be -57°C or higher so they boil. I cannot find any information about when CO2 becomes a gas believe it or not, so I am not sure what the air temp should be. does that sound like a workable "environment?"

thanks in advance for any help

Response by 1LT Private RallyPoint Member made Aug 28 at 2014 1:55 AM

2014-08-28T01:55:35-04:00

Dear Cpl Michael Strickler,

Carbon dioxide has no liquid state at pressures below 5.1 standard atmospheres (520 kPa). At 1 atmosphere (near mean sea level pressure), the gas deposits directly to a solid at temperatures below -78.5 °C ; -109.3 °F) and the solid sublimes directly to a gas above -78.5 °C. In its solid state, carbon dioxide is commonly called dry ice. Liquid carbon dioxide forms only at pressures above 5.1 atm; the triple point of carbon dioxide is about 518 kPa at -56.6 °C (see phase diagram). The critical point is 7.38 MPa at 31.1 °C. At temperatures and pressures above the critical point, carbon dioxide behaves as a supercritical fluid known as supercritical carbon dioxide.

Maybe liquid Ammonia? ( Melts @ -77.73 °C (-107.91 °F) Boils @ -33.34 °C (-28.01 °F)

Warmest Regards, Sandy

Reference: http://en.wikipedia.org/wiki/Carbon_dioxide

Response by 1SG Private RallyPoint Member made Aug 28 at 2014 2:59 AM

2014-08-28T02:59:01-04:00

Methane is a solid choice; it is both common (this situation actually exists on Titan, and postulated elsewhere) and fits your description.
It liquefies (assuming one atmosphere of pressure at a little cooler than you want (-164C) and freezes at -182C.
If you temperature range is fixed, a higher atmospheric pressure would raise the temperature to boil off the methane ocean.