Balanced equations establish ratios in moles between the compounds in the equation. Ex. 3 Fe + 4 H2O → Fe3O4 + 4 H2 3 mole Fe : 4 mole H2O : 1 mole Fe3O4 : 4 H2 The ratio between any two compounds in the equation can be written as a fraction Ex. 3 mol Fe or 4 mole H2O or 1 mole Fe3O4 4 mol H2 1 mole Fe3O4 3 mole Fe By using these mole-mole ratios and the molar mass ratios, we can solve many different kinds of problems! 1. How many moles of A are in x grams of A? Or how many grams of A are in x moles of A? Two-step problem (two parentheses), using the molar mass ratios. Ex. How many moles of Fe in 150 g of Fe? 2. How many moles of A does it take to make x moles of B? Two- step problem (two parentheses), uses the mole-mole ratios. Ex. How many moles of H2O does it take to rust 18 moles of Fe? 3. How many moles of A does it take to make x grams of B? Or how many grams of A does it take to make x moles of B? Three-step problem (three parentheses), will use the mole-mole ratios and the molar mass ratio. Ex. How many moles of H2O does it take to rust 18 grams of Fe? Ex. How many grams of H2O does it take to rust 18 moles of Fe? 4. How many grams of A does it take to make x grams of B? Four-step problem (4 parentheses), will use both the mole-mole ratios and the molar mass ratio. Ex. How many grams of water does it take to rust 18 grams of iron? Homework: Moles-Moles Ratios worksheet (below). The key is also given, so show your work for credit! |

Unit 4 – Chemical Reactions > Notes >