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Understanding Stoichiometry: Mass Relationships in Chemical Reactions

Stoichiometry is the branch of chemistry focused on mass relationships between elements in compounds and the interactions between reactants and products in chemical reactions. This includes both composition stoichiometry, dealing with elements in compounds, and reaction stoichiometry, which concerns the mass relationships during chemical transformations. By utilizing balanced equations, chemists can perform stoichiometric calculations to determine the amounts of substances involved in reactions, such as mole-to-mole conversions, to predict product formation accurately.

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Understanding Stoichiometry: Mass Relationships in Chemical Reactions

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  1. Chapter 12 Stoichiometry

  2. Stoichiometry The branch of chemistry that deals with the mass relationships of elements in compounds and the mass relationships between reactants and products in a chemical reaction.

  3. Composition Stoichiometry • Stoichiometry that deals with the mass relationships of elements in compounds

  4. Reaction Stoichiometry • Stoichiometry involving the mass relationships between reactants and products in a chemical reaction

  5. Equations are the recipes that tell chemists • what amounts of reactants to mix and • what amounts of products to expect. • The quantities of reactants and products -----come from the balanced equation.

  6. When you know the quantity (grams or moles) of one substance in a reaction, you can calculate the quantity of any other substance consumed or created in the reaction.

  7. Calculations using balanced equations are called stoichiometric calculations. For chemists, stoichiometry is a form of bookkeeping.

  8. N2(g) + 3H2(g) 2NH3(g) INTERPRETING CHEMICAL EQUATIONS 1 mol of nitrogen reacts with 3 mol of hydrogen -------to form 2 mol of ammonia.

  9. Reaction – Stoichiometry Problems • Begin with a balanced chemical equation!!!

  10. Mole-Mole Calculations • The coefficients from the balanced equation are used to write conversion factors called mole ratios.

  11. Three of the mole ratios for this equation are 1 mol N2 2 mol NH3 3 mol H2 3 mol H2 1 mol N2 2 mol NH3

  12. Reaction – Stoichiometry Problems • Identify the information given • Identify the unknown, the information you are expected to find. • Given  Unknown

  13. Given amount in moles Mole to Mole Ratio Unknown amount in moles

  14. From balanced equation b mol W xb a molG a x mol G x = mol W Thus a general solution for a mole-mole problem is given by Given Mole ratio Calculated

  15. 2 mol NH3 1 mol N2 How many moles of ammonia are produced when 0.60 mol of nitrogen reacts with hydrogen? 0.60 mol N2 x = 1.20 mol NH3 Given Mole Ratio

  16. Problem • In a spacecraft, the carbon dioxide exhaled by astronauts can be removed by its reaction with lithium hydroxide. • CO2(g) + 2 LiOH(s)  Li2CO3(s) + H2O (l) • How many moles of lithium hydroxide are required to react with 20 moles of CO2, the average amount exhaled by a person each day?

  17. Answer • 20 mole CO2 x 2 mole LiOH 1 mole CO2 = 40 mole LiOH

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