Decomposition Reaction Stoichiometry: Calculations and Examples

📚 Quick Study Guide

⚛️ Decomposition reactions involve breaking down a single reactant into two or more products.

🧪 The general form is: $AB \rightarrow A + B$

⚖️ Stoichiometry uses mole ratios from balanced equations to calculate the amounts of reactants and products.

🔢 Steps for Stoichiometry:
• ✏️ Balance the chemical equation.
• ⚖️ Convert given mass to moles (moles = mass / molar mass).
• ➗ Use the mole ratio from the balanced equation to find the moles of the desired substance.
• 📏 Convert moles back to mass (mass = moles * molar mass), if needed.

🧪 Practice Quiz

1. Which of the following is the general form of a decomposition reaction?
   1. $A + B \rightarrow AB$
   2. $AB \rightarrow A + B$
   3. $A + BC \rightarrow AC + B$
   4. $AB + CD \rightarrow AD + CB$
2. Calcium carbonate ($CaCO_3$) decomposes into calcium oxide ($CaO$) and carbon dioxide ($CO_2$). If you start with 50g of $CaCO_3$, how many moles of $CO_2$ will be produced? (Molar mass of $CaCO_3$ = 100 g/mol)
   1. 0.25 moles
   2. 0.5 moles
   3. 1 mole
   4. 2 moles
3. When potassium chlorate ($KClO_3$) is heated, it decomposes into potassium chloride ($KCl$) and oxygen gas ($O_2$). What is the mole ratio of $KClO_3$ to $O_2$ in the balanced equation?
   1. 1:1
   2. 2:3
   3. 3:2
   4. 1:2
4. Ammonium nitrate ($NH_4NO_3$) decomposes explosively into nitrogen gas ($N_2$), water ($H_2O$), and oxygen gas ($O_2$). If 80 grams of $NH_4NO_3$ decomposes completely, what is the mass of $N_2$ produced? (Molar mass of $NH_4NO_3$ = 80 g/mol, $N_2$ = 28 g/mol)
   1. 14 g
   2. 28 g
   3. 56 g
   4. 80 g
5. Mercury(II) oxide ($HgO$) decomposes into mercury ($Hg$) and oxygen ($O_2$). If you collect 1 mole of $O_2$, how many moles of $HgO$ were required?
   1. 0.5 moles
   2. 1 mole
   3. 2 moles
   4. 4 moles
6. A 100g sample of an unknown compound decomposes to produce 40g of oxygen gas. If the only other product is a metal oxide with a mass of 60g, what can you conclude about the original compound?
   1. It contained only the metal and oxygen.
   2. It contained other elements besides the metal and oxygen.
   3. It was pure oxygen.
   4. It was not a compound at all.
7. If 2 moles of $AB$ decompose according to the equation $AB \rightarrow A + B$, and the molar mass of $A$ is 10 g/mol, what mass of $A$ is produced?
   1. 5 g
   2. 10 g
   3. 20 g
   4. 40 g