# Stoichiometry Module 6.

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Stoichiometry Module 6

Mole Relationships in Chemical Equations
You do not always have stoichiometry problems where you are given the reactants and then asked for the product. You might be given the product and asked for the reactant.

Example Prob #1 2NaNO2 + O2  2NaNO3
How many moles of oxygen gas must you use in order to make 15.0 moles of NaNO3? NaNO2?

Limiting Reactants and Excess Components
Limiting reactant: the reactant in the equation that runs out first! This means that we only need to know the quantity of the limiting reactant because it will determine how much product can be formed in any reaction

Example Prob #2 The first step in the process that converts iron ore into pure iron involves converting iron ore into iron oxide. 4FeS2 + 11O2  2Fe2O3 + 8SO2 Iron ore Iron Oxide If an iron manufacturer starts with 1,256.0 moles of iron ore, how many moles of oxygen will be needed to react completely with the iron ore? How may moles of iron oxide will be made?

Relating Products to Reactants in Chemical Equations
How do we know how much of a reactant we need to make a certain amount of product? We need to find out the minimum reactants needed to reach our desired product.

Example Prob #3 Citric acid (C6H8O7), a component of fruit drinks, jams, and jellies, is produced using the following reaction: C12H22O11 + H2O + 3O2 2C6H8O7 + 4H2O If a fruit drink manufacturer decides she needs 1.4 x 105 moles of citric acid, what is the minimum reactants?

Limiting Reactant is Identified
Stoichiometry can be used to determine the products when the limiting reactant is given!

Excess Reactant Excess Reactant: when a chemist adds a lot of extra reactant to make sure that the other reactant is the limiting reactant

Example Prob #4 Calcium chloride 6-hydrate (CaCl2H12O6) is a substance used to melt snow on streets and sidewalks. It is made from calcium carbonate (CaCO3) using the following reaction: CaCO3 + 2HCl + 5H2O  CaCl2H12O6 + CO2 If 3.49 moles of HCl are added to excess CaCO3 and excess water, how many moles of calcium chloride 6-hydrate will be made?

Stoichiometric Coefficients
the number of molecules which participate in the reaction as written 2H2 + O2  2H2O

Gay-Lussac’s Law The stoichiometric coefficients in a chemical equation relate the volume of gases in equation as well as the number of moles of substances in the equation REMEMBER: This law can only be used in problems that only have gases!!!

Example Prob #5 A chemist decides to produce carbon dioxide gas using the following reaction: Na2CO3 (s) + 2HCl (g)  2NaCl (s) + CO2(g) + H2O (g) If the chemist wants to make 3.67 liters of CO2 gas, how many liters of HCl gas must be used?