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

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

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

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

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 55.85 𝑔 =0.0619 mol Fe According to our ratios 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒 2 𝑂 3 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒 = 2 4 = 𝑥 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒 2 𝑂 3 0.0619 𝑚𝑜𝑙 𝐹𝑒 𝑥 = 2 4 ×0.0619 𝑚𝑜𝑙 𝐹𝑒 = 0.031 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒 2 𝑂 3 0.031 𝑚𝑜𝑙𝑒𝑠 𝐹𝑒 2 𝑂 3 × 159.69 𝑔 1 𝑚𝑜𝑙 𝐹𝑒 2 𝑂 3 =4.95 g 𝐹𝑒 2 𝑂 3

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