Chem 20 Review: Stoichiometry

1. Chem 20 Review: Stoichiometry

2. Mole Ratios • Mole ratios will be used in every stoichiometry question so it is important that we understand how they work • Mole ratios are derived from the COEFFICIENTS of a BALANCED CHEMICAL EQUATION • Please follow along with the example on the following slide

3. i.e.: 2 H2 + O2 2 H2O • Ratio of H2 to O2 = 2:1 or 2 1 • For every 2 moles of H2, there is 1 mole of O2 • Ratio of H2 to H2O = 2:2 or 2 or 1 2 1 • For every 2 moles of H2, there are 2 moles of H2O *It can also be inverted depending on what you are comparing* • Ratio of O2 to H2 = 1:2 or 1 2 • For every 1 mole of O2, there are 2 moles of H2 • Ratio of H2O to H2 = 2:2 or 2 or 1 2 1 • For every 2 moles of H2O, there are 2 moles of H2

4. 4 Steps for Solving ANY Stoichiometry Question • 1) Write a BALANCED chemical equation • 2) Take whatever value is GIVEN in the question and CONVERT IT TO MOLES • 3) Use the MOLAR RATIOS from the balanced chemical equation to identify the number of moles for the chemical you need • 4) Go where the question asks using the REBALANCED EQUATION

5. Example: • What mass of oxygen gas will react with 15.0g of hydrogen gas and what mass of water will be produced?