Solving Stoichiometry Problems Objectives:     1.    Name four major categories of stoichiometry problems.     2.    Explain how to solve each type of stoichiometry problems. Notes: It is important to remember that solving stoichiometry problems is very similar to following a recipe.  Once you know the recipe you can modify it using the same ratios to make the product for more or less people. There are 4 major categories of stiochiometry problems.  It is important to remember, though, that in every situation you need to start out with a balanced equation. 1.    Mole-Mole Problems Problem:  How many moles of HCl are needed to react with 0.87 moles of Al?         Step 1: Balance The Equation & Calculate the Ratios             2Al:6HCl (1:3)        2Al:2AlCl3 (1:1)        2Al:3H2 (1:1.5)         Step 2:  Find the Moles of the Given             0.87 moles of aluminum are reacted with hydrochloric acid           Step 3: Calculate the moles using the ratios            moles HCl = 0.87molAl x  3molHCl/1molAl = 2.6 mol HCl               2.    Mass-Mass Problems (Strategy: Mass g Mole g Mole g Mass) Problem:  How many grams of Al can be created decomposing 9.8g of  Al2O3?         Step 1: Balance The Equation & Calculate the Ratios               2Al2O3:4Al (1:2)        2Al2O3:3O2 (1:1.5) Step 2:  Find the Mass of the Given             9.8g Al2O3 are decomposed Step 3: Calculate the moles of the given (mol/g)             9.8g Al2O3 x (1mol Al2O3/102g Al2O3) = 0.096 mol Al2O3           Step 4: Calculate the moles using the ratios         0.096 mol Al2O3 x (2 mol Al/1 mol Al2O3) = 0.19 mol Al                 Step 5: Calculate the mass using the new moles         0.19 mol Al x (27g Al/1 mol Al) = 5.1g Al           3.    Mass-Volume Problems (Strategy: Mass g Mole g Mole g Volume)         Problem:  How many liters of H2 are created from the reaction of 20.0g K?         Step 1: Balance The Equation & Calculate the Ratios               2K:2H2O (1:1)    2K:2KOH (1:1)    2K:1H2 (2:1) Step 2:  Find the Mass of the Given             20.0g K are used in the reaction Step 3: Calculate the moles of the given (mol/g)             20.0g K x (1 mol K / 39g K) = 0.513 mol K             Step 4: Calculate the moles using the ratios             0.51 mol K x (1mol H2 /2mol K) = 0.266mol H2                     Step 5: Calculate the volume using the new moles         0.266 mol H2 x (22.4L H2 /1mol H2) = 5.75L H2         4.    Volume-Volume Problems         Problem:  How many liters of SO2 will be produced from 26.9L O2? Step 1: Balance The Equation & Calculate the Ratios             2O2:1S2 (2:1)    2O2:2SO2 (1:1)     Step 2: Find the volume of the given             26.9L O2 Step 3: Calculate the moles of the given             26.9L O2 x (1 mol O2 / 22.4L) = 1.20 mol O2         Step 4: Calculate the moles using the ratios             1.20 mol O2 x (1mol SO2 /1mol  O2) = 1.20 mol SO2                 Step 5: Calculate the volume using the new moles         1.20 mol O2 x (1mol SO2 /1mol  O2) x (22.4L /1mol) = 26.9L SO2