Thread: Ammonia

Hello :-D
COuld somebody please provide me with the density for solid and liquid ammonia. I've tried to find at Google, but failed.

depends on the temperature

681.9Kg/M3 @ -33.3 C

817 to 820 kg/M3 @ -80C depending if its crystals or transparent solid.

Ok,thanks.
How come ammonia doesn't behave the same way as water when it freezes (i.e. its density decreases)?
After all each ammonia molecule binds to four other, just as each water molecule binds to four other water molecules.

unusual behavior has its origin in the structure of the water molecule. There is a strong tendency to form a network of hydrogen bonds, where each hydrogen atom is in a line between two oxygen atoms. This hydrogen bonding tendency gets stronger as the temperature gets lower (because there is less thermal energy to shake the hydrogen bonds out of position). The ice structure is completely hydrogen bonded, and these bonds force the crystalline structure to be very "open", as shown in the following picture:
Picture credits

In the following two pictures, the first shows a typical structure of liquid water, while the second is an ice structure; note the extra open space in the ice.


It is this open solid structure that causes ice to be less dense than liquid water. That is why ice floats on water, for which we should all be thankful because if water behaved "normally" many bodies of water would freeze solid in the winter, killing all the life within them.

Water's "density maximum" is a product of the same phenomenon. Close to the freezing point, the water molecules start to arrange locally into ice-like structures. This creates some "openness" in the liquid water, which tends to decrease its density. This is opposed by the normal tendency for cooling to increase the density; it is at approximately 4 degrees Celsius that these opposing tendencies are balanced, producing the density maximum.

Updated April 21, 2000

How come ammonia molecules aren't arranged the same way?
Is it because the hydrogen bonds are not equalle strong (because of ammonia's lower electronegativity)?

It can't form the same geometric structure, NH3 is like a tripod, H2O is a bent line.

Ok, thanks.