1. Reaction Stoichiometry
Balance a chemical reaction, using conservation of mass and experimental data

2. Conservation of Mass Matter cannot be created or destroyed
Mass of reactants = mass of products
The number and type of each atom present before reaction = number of type of atoms present after reaction
Conservation of Mass

3. Reaction of Iron with Oxygen to make rust
When Iron is reacted with Oxygen gas (O2) it makes Iron(III)oxide (Fe2O3)
The Law of the conservation of mass requires
#Fe atoms in the reactants = #Fe atoms in the product
#O atoms in the reactants = #O atoms in the product
We must find whole numbers (stoichiometric coefficients) for each reactant and product so that at the end the number of atoms of each type obey this condition
__Fe + __O2 → ____ Fe2O3
4Fe + 3O2 → 2 Fe2O3

4. Stoichiometric Coefficients
4Fe + 3O2 → 2 Fe2O3
The coefficients 4, 3 and 2 are the required ratios of reactants needed to make a certain amount of product
For example 4 dozen Fe atoms: 3 dozen O2 make 2 dozen Fe2O3
4 moles Fe atoms: 3 moles O2 make 2 moles Fe2O3
But 4 g Fe: 3 g O2 does not make 2g Fe2O3 since 7 g ≠2 g

5. Confirming 4Fe + 3O2 → 2 Fe2O3 is correct
We can confirm our reaction is true by combining the reactants in the correct ratio and see if we made the correct amount of product
Let’s say we have 3.46 g of Fe
3.46𝑔× 1 𝑚𝑜𝑙 𝐹𝑒 𝑔 = mol Fe
According to our ratios
𝑚𝑜𝑙𝑒𝑠 𝐹𝑒 2 𝑂 3 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒 = 2 4 = 𝑥 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒 2 𝑂 𝑚𝑜𝑙 𝐹𝑒
𝑥 = 2 4 × 𝑚𝑜𝑙 𝐹𝑒 = 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒 2 𝑂 3
0.031 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒 2 𝑂 3 × 𝑔 1 𝑚𝑜𝑙 𝐹𝑒 2 𝑂 3 =4.95 g 𝐹𝑒 2 𝑂 3

6. Tonight’s Experiment
Thermal decomposition of potassium chlorate above 356oC
___𝐾𝐶𝑙𝑂 3 (𝑠) → ___𝐾𝐶𝑙 (𝑠) +____ 𝑂 2 (𝑔)
Balance the reaction using the law of mass conservation and determine KClO3 : KCl : O2
Measure mass of KClO3 and determine the number the number of moles KClO3
Measure the mass of the KCl product and determine the number of moles of KCl
Determine the experimental ratio moles KClO3 : moles KCl