Exactly of pure dry ammonia () gas was taken in a sealed eudiometer tube and subjected to prolonged — States of Matter and Gaseous State Chemistry Question
Question
Exactly $40\text{ mL}$ of pure dry ammonia ($NH_3$) gas was taken in a sealed eudiometer tube and subjected to prolonged electric sparks until complete dissociation occurred. Assuming the temperature and pressure are restored to their initial constant values, calculate the exact absolute increase in the total gas volume (in $\text{mL}$) due to this dissociation.
💡 Solution & Explanation
The balanced chemical equation for the dissociation of ammonia is $2NH_3(g) \rightarrow N_2(g) + 3H_2(g)$. According to Gay-Lussac's law of combining volumes, 2 volumes of $NH_3$ completely dissociate to yield 1 volume of $N_2$ and 3 volumes of $H_2$, giving a total of 4 volumes of product gases. If we start with $40\text{ mL}$ of $NH_3$, the volume of $N_2$ formed is $20\text{ mL}$ and the volume of $H_2$ formed is $60\text{ mL}$. The final total volume = $20 + 60 = 80\text{ mL}$. The absolute increase in volume = Final Volume - Initial Volume = $80 - 40 = 40\text{ mL}$.