# Is NH_3 a gas or a solid? How do you know?

Jun 15, 2018

Well, it's a gas... how do I know? I've smelled it passing by, after seeing a student react a mixture of cations (containing ${\text{NH}}_{4}^{+}$, ${\text{Mn}}^{2 +}$, ${\text{Fe}}^{3 +}$, ${\text{Ag}}^{+}$, ${\text{Ni}}^{2 +}$, and ${\text{Al}}^{3 +}$) with $\text{NaOH}$.

The $\text{NaOH}$ reacted with the ${\text{NH}}_{4}^{+}$ (and with some of the other cations) to produce a gas that smelled like cleaning products...

$\text{NH"_4^(+)(aq) + "NaOH"(aq) -> "NH"_3(g) + "Na"^(+)(aq) + "H"_2"O} \left(l\right)$

It formed as a gas, since its boiling point at $\text{1 atm}$ is only $- {33}^{\circ} \text{C}$. It spontaneously vaporizes under these conditions, if it were somehow obtained as a liquid.

A bit hard to read, but this is the best phase diagram I could find:

The $P T$ projection (purple) shows that at $\text{1 atm}$ (${\log}_{10} \left(P / \text{MPa}\right) \approx - 1$) and $\text{300 K}$, we are beneath the bottom purple curve, which divides the liquid (above) from the gas (below) regions.

Hence, at $\text{1 atm}$ and $\text{300 K}$, ammonia is certainly a gas.