Question

${(N{H_4})_2}C{r_2}{O_7}\xrightarrow{{heat}}{N_2}(g) + 4{H_2}O(g) + C{r_2}{O_3}$ What is the volume in litres of $d{m^3}$of ${N_2}$ evolved when $63g$ of ammonium dichromate is heated at STP?

Answer 1

Hint: As we know that at standard condition of temperature and pressure the volume released by the heating of reactant is equivalent to $22.4$ litres for one mole of any ideal gas. We can calculate the moles and then multiply this with $22.4$ litres or we can just multiply it with mass of the given compounds.

Complete Step by step answer: ${(N{H_4})_2}C{r_2}{O_7}\xrightarrow{{heat}}{N_2}(g) + 4{H_2}O(g) + C{r_2}{O_3}$
As we can see in the given equation that one mole of ammonium dichromate ${(N{H_4})_2}C{r_2}{O_7}$ upon heating gives one mole of nitrogen, one mole of chromate and four moles of water. In terms of their atomic mass we can say that $252g$ of ${(N{H_4})_2}C{r_2}{O_7}$ gives $28g$ nitrogen, $152g$ chromate and $72g$ water.
At standard conditions of temperature and pressure, we know that a compound on combustion releases $22.4$litres of main product. So, $252g$ of ammonium dichromate will release $22.4$litres of nitrogen gas at ST, similarly, if $63g$ of ammonium dichromate is heated at STP the nitrogen evolved will be equal to:
$\dfrac{{63 \times 22.4}}{{252}} = 5.59l$ which is approximately equal to $6L$ or in cubic decimetre $6\;d{m^3}$.

Additional information: Ammonium dichromate is a strong oxidising agent and when it is heated, it decomposes to green coloured chromium oxide crystals in air and gives off orange sparks which looks like a mini volcanic eruption and due to this ammonium dichromate is sometimes called Vesuvian fire. It is an extremely exothermic reaction. It is also used to demonstrate volcanic eruptions in school and college projects. But it is a carcinogenic compound hence its use is decreased at schools and college level. It was early used in pyrotechnics as well as in photography.

Note: Ammonium dichromate is considered a good source of nitrogen production laboratories as well as a catalyst. It is an oxidising agent and can react violently with any reducing agent. It is a strong irritant and highly toxic. It reacts to produce nitrogen and chromate.