Question

If a mixture containing $3$ moles of hydrogen and $1$ mole of nitrogen is converted completely into ammonia, the ratio of initial and final volumes under the same temperature and pressure would be:
A. $3:1$
B. $1:3$
C. $2:1$
D. $1:2$

Answer 1

We know that the ratio initial and final volume of the reaction is the ratio of the volume of reactants taken to start the reaction to the volume of product formed in the chemical reaction.

Complete step by step answer:
The balanced chemical equation representing the reaction between hydrogen and nitrogen is as follows.
$N_{2}(g)+3H_{2}(g) \to 2NH_{3}(g)$
According to the given data, the $3$ moles of hydrogen and $1$ mole of nitrogen is taken. Therefore, the total initial volume of the reaction is $4$.
It is given in the question that the mixture is converted completely into ammonia. It means that there is no limiting reagent in the reaction. That is each of the reactants is completely consumed in the reaction. Therefore, we can say that according to the balanced chemical equation, the final volume of the reaction is $2$.
Therefore, we can take the ratio of initial and final volumes as $4:2=2:1$.

Therefore, the correct option is option (C).

Note: We know that the chemical reaction is balanced in such a way that each and every kind of atom on the other side of the chemical equation are in the same number so that in accordance with the law of mass of conservation of the total mass of the reactant and that of the product becomes equal. It is also known that, when there is no such reactant left unreacted after reaction, the reaction gets completed and said to be economically friendly.