Question

which of the following is the correct way to describe the ratio of volumes of the substances in the chemical equation?
$2\ce{nh_3(g)} \
ightarrow \ce{n_2(g)} + 3\ce{h_2(g)}$
$2\ce{ l nh_3} : 1\ce{ l n_2} : 3\ce{ l h_2}$
$2\ce{ molecules nh_3} : 1\ce{ mole n_2} : 3\ce{ formula units h_2}$
$3\ce{ l nh_3} : 2\ce{ l n_2} : 2\ce{ l h_2}$
$3\ce{ moles nh_3} : 1\ce{ mole n_2} : 3\ce{ moles h_2}$

Explanation:

For gaseous substances at the same temperature and pressure, the volume ratio is equal to the mole ratio (from Avogadro's law). The balanced chemical equation \( 2\text{NH}_3(\text{g})
ightarrow \text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \) gives the mole ratio of \( \text{NH}_3 : \text{N}_2 : \text{H}_2 = 2:1:3 \). So the volume ratio should also be \( 2 \, \text{L NH}_3 : 1 \, \text{L N}_2 : 3 \, \text{L H}_2 \). The other options either have incorrect ratios or mix units (like molecules with moles/formula units) or wrong volume ratios.

Answer:

A. \( 2 \, \text{L NH}_3 : 1 \, \text{L N}_2 : 3 \, \text{L H}_2 \)