Question

there are three sets of sketches below, showing the same pure molecular compound (ammonia, molecular formula $nh_{3}$) at three different temperatures. the sketches are drawn as if a sample of ammonia were under a microscope so powerful that individual atoms could be seen. only one sketch in each set is correct. use the slider to choose the correct sketch in each set. you may need the following information:
melting point of $nh_{3}$: $-77.7^{circ}c$
bolling point of $nh_{3}$: $-33.3^{circ}c$
a
b
c
(choose one)
(choose one)
(choose one)

1. $^{circ}c$

-58. $^{circ}c$
-100. $^{circ}c$

Explanation:

1. For \(71^\circ \text{C}\): The temperature \(71^\circ \text{C}\) is above the boiling point of \(\ce{NH_3}\) (\(-33.3^\circ \text{C}\)), so ammonia is in the gas phase. Gas particles are far apart and move freely, so the sketch for \(71^\circ \text{C}\) (set A) should show widely spaced \(\ce{NH_3}\) molecules.
2. For \(-58^\circ \text{C}\): The temperature \(-58^\circ \text{C}\) is between the melting point (\(-77.7^\circ \text{C}\)) and boiling point (\(-33.3^\circ \text{C}\)) of \(\ce{NH_3}\), so ammonia is in the liquid phase. Liquid particles are close together but can move past each other, so the sketch for \(-58^\circ \text{C}\) (set B) should show \(\ce{NH_3}\) molecules closer than in gas but not in a fixed lattice.
3. For \(-100^\circ \text{C}\): The temperature \(-100^\circ \text{C}\) is below the melting point of \(\ce{NH_3}\) (\(-77.7^\circ \text{C}\)), so ammonia is in the solid phase. Solid particles are in a fixed, ordered lattice, so the sketch for \(-100^\circ \text{C}\) (set C) should show \(\ce{NH_3}\) molecules in a regular, close - packed arrangement.

Answer:

• For \(71^\circ \text{C}\) (set A): The sketch representing gas (widely spaced \(\ce{NH_3}\) molecules).
• For \(-58^\circ \text{C}\) (set B): The sketch representing liquid ( \(\ce{NH_3}\) molecules close together but mobile).
• For \(-100^\circ \text{C}\) (set C): The sketch representing solid ( \(\ce{NH_3}\) molecules in a fixed lattice).