Chemistry (gas)

Question

8. Besides using NaN3, there are a number of chemical reactions that produce N2 gas. One such example is,

NH4ClO4(s) + heat = N2(g) + Cl2(g) + O2(g) + H2O(l)

a) How many grams of ammonium perchlorate would you need to produce enough nitrogen gas to exactly fill a 67.2 L air-bag under standard conditions? (Hint: Begin by balancing equation.) (3 marks)

b) Would it be a good idea to use ammonium perchlorate in commercial airbags? Explain.

(1 mark)

Answer 1

Okay so the problem suggests that we start with balancing the chemical equation; so why don't we start there? If we look at the equation none of the elements are balanced. Oxygen is also in two of the products which will make it trickier to balance, so lets ignore it for now. As Hydrogen is tied to one of those products lets also ignore it for a second. That leaves nitrogen and chlorine. Both of them have 2 atoms/units (sorry not sure what term your class is using) in the product, but one in the reactant. So lets start with doubling the reactant and see where that gets us. I'll be ignoring the heat portion as it doesn't contribute to chemical balance.

2 NH4ClO4 --> N2 + Cl2 + O2 + H2O.

Okay so that solved the nitrogen and the chlorine, but hydrogen and oxygen are still a problem. Let's focus on hydrogen next as there is only one compound on each side that has hydrogen as part of the chemical formula. Currently there are 8 H atoms on the left, while there are 2 H atoms on the right. If we form 4 water molecules we can balance that out to make the following equation.

2 NH4ClO4 --> N2 + Cl2 + O2 + 4 H2O.

Okay so far it's looking good. We have everything balanced but oxygen. We currently have 8 O atoms on the left and 6 O atoms ( 1 O2 + 4 H2O) on the right. That's a problem. Luckily we have a compound that is only O atoms and two of them! So if we double the number of Oxygen atoms we would get the following balanced equation.

2 NH4ClO4 --> N2 + Cl2 + 2 O2 + 4 H2O.

Great lets move on to the problem at hand. It immediately looks like it should be an ideal gas law problem with PV = nRT. But wait! All we need is the moles of the gas produced and we have the volume of the gas produced.

One rule of STP is that 1 mol of gas = 22.4 L of gas.

So if we use this we know we need 3 mol of N2 gas to make 67.2 L of N2. Using the stoichiometry we already determined we know that we need 6 mols of NH4ClO4 so that we can produce 3 mols of N2 gas. Using the molecular mass of NH4ClO4 (117.49) we get that we would need 704.94 g of the reactant. However there were only 3 significant figures in the problem so we must report it as 705 g of ammonium nitrate.

Sorry forgot the second question hence the edit. No this is not a safe compound for air bags. Cl2 gas is a toxic gas that is dangerous.