Two volumes of an oxide of nitrogen decomposed in the presence of a heated catalyst to form two volumes of nitrogen gas and one volume of oxygen gas, all volumes measured at the same conditions of temperature and pressure - Leaving Cert Chemistry - Question g - 2021

To determine the formula of the nitrogen oxide that decomposed, we can start by considering the reaction:

$2 \text{NO}_x \rightarrow 2 \text{N}_2 + \text{O}_2$

From the balanced equation, we see that for every 2 volumes of the nitrogen oxide (NO_x), we are producing 2 volumes of nitrogen (N2) and 1 volume of oxygen (O2). This can be interpreted as:

• For every 2 volumes of the nitrogen oxide, we end up with 2 volumes of N2 and 1 volume of O2, which leads us to formulate the reaction in terms of volumes.

Given that the reaction loses one volume of the nitrogen compound and gains one volume of O2, we deduce that:

• The ratio of nitrogen to oxygen in the original compound must correspond to that of nitrogen in N2 and oxygen in O2.

This suggests the decomposition results in a nitrogen oxide of the form:

$\text{NO}$