Question

Redox reaction involves transfer of electrons between 2 chemical species. An unbalanced and incomplete example is shown below:
$N_2+H_{3}P{O}_2\to H{N}_3+P_4{O}_6$

If the above reaction were unidirectional towards right, what fraction of $P_4{O}_6$ would be left unreacted if reaction were started with stoichiometric amount of reactants.

• A. $\frac{1}{2}$
• B. $\frac{3}{4}$
• C. $\frac{1}{3}$
• D. $\frac{2}{3}$

Answer 1

The correct option is D $\frac{2}{3}$

$12N_2+4H_{3}P{O}_2\to 8H{N}_3+(P_4{O}_6+2H_{2}O)$
$P_4{O}_6+6H_{2}O\to 4H_{3}P{O}_3$
6 moles $H_{2}O$ reacts with 1 mole $P_4{O}_6$
2 moles $H_{2}O$ reacts with $\frac{1\times 2}{6}=\frac{1}{3}$ mole $P_4{O}_6$
$\therefore$ fraction of $P_4{O}_6$ left unreacted $=\frac{2}{3}$