Using a chemical equation to find moles of product

Question

Ammonium perchlorate NH4ClO4 is a powerful solid rocket fuel, used in the Space Shuttle boosters. It decomposes into nitrogen N2 gas, chlorine Cl2 gas, oxygen O2 gas and water vapor, releasing a great deal of energy. Calculate the moles of chlorine produced by the reaction of 0.085mol of ammonium perchlorate. Be sure your answer has a unit symbol, if necessary, and round it to the correct number of significant digits. 

Answer 1

Since we are trying find out how many moles of chlorine gas we end up with, we will need to make sure we have the correct mole ratio of products to reactants. Always start with a properly balanced equation.

2 NH₄ClO₄ → N₂ + Cl₂ + 2 O₂ + 4 H₂O

Note the ratio of moles of chlorine gas to moles of ammonium perchlorate is 1:2

We will use this ratio along with dimensional analysis to find our answer.

0.085 mol NH4ClO4 x (1 mol Cl₂/2 mol NH₄ClO₄) = 0.043 mol Cl₂

So to get 1 mole of chlorine gas, 2 moles of ammonium perchlorate must react. Therefore, however many moles of ammounium perchlorate you start with, then you will end up with half as many moles in chlorine gas.

Answer 2

2NH₄ClO₄ ===> N₂ + Cl₂ + 2O₂ + 4H₂O + energy ... balanced equation

0.085 moles NH₄ClO₄ x 1 mole Cl₂/2 mole NH₄ClO₄ = 0.0425 moles = 0.043 moles Cl₂ produced (2 sig.figs.)